<PAGE>   1
                                                                  EXHIBIT 4.3.20


THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY OTHER
SECURITIES LAWS, HAVE BEEN TAKEN FOR INVESTMENT, AND MAY NOT BE SOLD OR
TRANSFERRED OR OFFERED FOR SALE OR TRANSFER UNLESS A REGISTRATION STATEMENT
UNDER THE SECURITIES ACT AND OTHER APPLICABLE SECURITIES LAWS WITH RESPECT TO
SUCH SECURITIES IS THEN IN EFFECT, OR IN THE OPINION OF COUNSEL (WHICH OPINION
IS REASONABLY SATISFACTORY TO THE ISSUER OF THESE SECURITIES), SUCH REGISTRATION
UNDER THE SECURITIES ACT AND OTHER APPLICABLE SECURITIES LAWS IS NOT REQUIRED.

      Class: AE             Date: November 29, 2000         Warrant to Purchase
                                                                ________ Shares

                                   ----------

             (Incorporated under the laws of the State of Delaware)

                      WARRANT FOR THE PURCHASE OF SHARES OF

                THE $.001 PAR VALUE COMMON STOCK OF PROBEX CORP.

    Warrant Price: $1.40 per share, subject to adjustment as provided below.


      THIS IS TO CERTIFY that, for value received, _______________ and its
registered assigns (collectively, the "Holder"), is entitled to purchase,
subject to the terms and conditions hereinafter set forth, up to _________
Shares of the $.001 par value common stock ("Common Stock") of Probex Corp., a
Delaware corporation (the "Company"), and to receive certificate(s) for the
Common Stock so purchased.

      1. EXERCISE PERIOD AND VESTING. The exercise period is the period
beginning on the date of this Warrant (the "Issuance Date") and ending at 11:59
p.m. Central Standard Time, on November 28, 2005 (the "Exercise Period"). This
Warrant will terminate automatically and immediately upon the expiration of the
Exercise Period.

      2. EXERCISE OF WARRANT; CASHLESS EXERCISE. This Warrant may be exercised,
in whole or in part, at any time and from time to time during the Exercise
Period. Such exercise shall be accomplished by tender to the Company of the
purchase price set forth above as the warrant price (the "Warrant Price"),
either (a) in cash, by wire transfer or by certified check or bank cashier's
check, payable to the order of the Company, or (b) by surrendering such number
of shares of Common Stock received upon exercise of this Warrant with a current
market price equal to the Warrant Price (a "Cashless Exercise"), together with
presentation and surrender to the Company of this Warrant with an executed
subscription in substantially the form attached hereto as Exhibit A (the
"Subscription"). Upon receipt of the foregoing, the Company will deliver to the
Holder, as promptly as possible, a certificate or certificates representing the
shares of Common Stock so purchased, registered in the name of the Holder or its
transferee (as permitted under Section 3 below). With respect to any exercise of
this Warrant, the Holder will



<PAGE>   2

for all purposes be deemed to have become the holder of record of the number of
shares of Common Stock purchased hereunder on the date this Warrant, a properly
executed Subscription and payment of the Warrant Price is received by the
Company (the "Exercise Date"), irrespective of the date of delivery of the
certificate evidencing such shares, except that, if the date of such receipt is
a date on which the stock transfer books of the Company are closed, such person
will be deemed to have become the holder of such shares at the close of business
on the next succeeding date on which the stock transfer books are open.
Fractional shares of Common Stock will not be issued upon the exercise of this
Warrant. In lieu of any fractional shares that would have been issued but for
the immediately preceding sentence, the Holder will be entitled to receive cash
equal to the current market price of such fraction of a share of Common Stock on
the trading day immediately preceding the Exercise Date. In the event this
Warrant is exercised in part, the Company shall issue a new Warrant to the
Holder covering the aggregate number of shares of Common Stock as to which this
Warrant remains exercisable for. The Company acknowledges and agrees that this
Warrant was issued on the Issuance Date.

      If the Holder elects to conduct a Cashless Exercise, the Company shall
cause to be delivered to the Holder a certificate or certificates representing
the number of shares of Common Stock computed using the following formula:

         X = Y (A-B)
               -----
                 A

         Where:

                    X    =   the number of shares of Common Stock to be issued
                             to Holder;

                    Y    =   the portion of the Warrant (in number of shares
                             of Common Stock) being exercised by Holder (at the
                             date of such calculation);

                    A    =   the fair market value of one share of Common
                             Stock on the Exercise Date (as calculated below);
                             and

                    B    =   Warrant Price (as adjusted to the date of such
                             calculation).

      For purposes of the foregoing calculation, "fair market value of one share
of Common Stock on the Exercise Date" shall mean: (i) if the principal trading
market for such securities is a national or regional securities exchange, the
average closing price on such exchange for the ten (10) trading days immediately
prior to such Exercise Date; (ii) if sales prices for shares of Common Stock are
reported by the Nasdaq National Market System or Nasdaq Small Cap Market (or a
similar system then in use), the average last reported sales price for the ten
(10) trading days immediately prior to such Exercise Date; or (iii) if neither
(i) nor (ii) above are applicable, and if bid and ask prices for shares of
Common Stock are reported in the over-the-counter market by Nasdaq (or, if not
so reported, by the National Quotation Bureau), the average of the high bid and
low ask prices so reported for the ten (10) trading days immediately prior to
such Exercise Date. Notwithstanding the foregoing, if there is no reported
closing price, last reported sales price, or bid and ask prices, as the case may
be, for the period in question, then the




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current market price shall be determined as of the latest ten (10) day period
prior to such day for which such closing price, last reported sales price, or
bid and ask prices, as the case may be, are available, unless such securities
have not been traded on an exchange or in the over-the-counter market for 30 or
more days immediately prior to the day in question, in which case the current
market price shall be determined in good faith by, and reflected in a formal
resolution of, the Board of Directors of the Company. The Company acknowledges
and agrees that this Warrant was issued on the Issuance Date.

      3.  TRANSFERABILITY AND EXCHANGE.

         (a) This Warrant, and the Common Stock issuable upon the exercise
hereof, may not be sold, transferred, pledged or hypothecated unless the Company
shall have been provided with an opinion of counsel, or other evidence,
reasonably satisfactory to it, that such transfer is not in violation of the
Securities Act, and any applicable state securities laws. Subject to the
satisfaction of the aforesaid condition, this Warrant and the underlying shares
of Common Stock shall be transferable from time to time by the Holder upon
written notice to the Company. If this Warrant is transferred, in whole or in
part, the Company shall, upon surrender of this Warrant to the Company, deliver
to each transferee a Warrant evidencing the rights of such transferee to
purchase the number of shares of Common Stock that such transferee is entitled
to purchase pursuant to such transfer. The Company may place a legend similar to
the legend at the top of this Warrant on any replacement Warrant and on each
certificate representing shares issuable upon exercise of this Warrant or any
replacement Warrants. Only a registered Holder may enforce the provisions of
this Warrant against the Company. A transferee of the original registered Holder
becomes a registered Holder only upon delivery to the Company of the original
Warrant and an original Assignment, substantially in the form set forth in
Exhibit B attached hereto.

         (b) This Warrant is exchangeable upon its surrender by the Holder to
the Company for new Warrants of like tenor and date representing in the
aggregate the right to purchase the number of shares purchasable hereunder, each
of such new Warrants to represent the right to purchase such number of shares as
may be designated by the Holder at the time of such surrender.

      4. ADJUSTMENTS TO WARRANT PRICE AND NUMBER OF SHARES SUBJECT TO WARRANT.
The Warrant Price and the number of shares of Common Stock purchasable upon the
exercise of this Warrant are subject to adjustment from time to time upon the
occurrence of any of the events specified in this Section 4.

         (a) In case the Company shall (i) pay a dividend or make a distribution
in shares of Common Stock or other securities, (ii) subdivide its outstanding
shares of Common Stock into a greater number of shares, (iii) combine its
outstanding shares of Common Stock into a smaller number of shares, or (iv)
issue by reclassification of its shares of Common Stock other securities of the
Company, then the Warrant Price in effect at the time of the record date for
such dividend or on the effective date of such subdivision, combination or
reclassification, and/or the number and kind of securities issuable on such
date, shall be proportionately adjusted so that the Holder of any Warrant
thereafter exercised shall be entitled to receive the aggregate number and kind
of



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shares of Common Stock (or such other securities other than Common Stock) of the
Company, at the same aggregate Warrant Price, that, if such Warrant had been
exercised immediately prior to such date, the Holder would have owned upon such
exercise and been entitled to receive by virtue of such dividend, distribution,
subdivision, combination or reclassification. Such adjustment shall be made
successively whenever any event listed above shall occur.

         (b) In case the Company shall fix a record date for the making of a
distribution to all holders of Common Stock (including any such distribution
made in connection with a consolidation or merger in which the Company is the
surviving corporation) of cash, evidences of indebtedness or assets, or
subscription rights or warrants, the Warrant Price to be in effect after such
record date shall be determined by multiplying the Warrant Price in effect
immediately prior to such record date by a fraction, the numerator of which
shall be the current market price per share of Common Stock on such record date,
less the amount of cash so to be distributed (or the fair market value (as
determined in good faith by, and reflected in a formal resolution of, the Board
of Directors of the Company) of the portion of the assets or evidences of
indebtedness so to be distributed, or of such subscription rights or warrants,
applicable to one share of Common Stock, and the denominator of which shall be
such current market price per share of Common Stock. Such adjustment shall be
made successively whenever such a record date is fixed; and in the event that
such distribution is not so made, the Warrant Price shall again be adjusted to
be the Warrant Price which would then be in effect if such record date had not
been fixed.

         (c) For the purpose of any computation under any subsection of this
Section 4, the "current market price" per share of Common Stock on any date
shall be the per share price of the Common Stock on the trading day immediately
prior to the event requiring an adjustment hereunder, which per share price
shall be: (i) if the principal trading market for the Common Stock is a national
or regional securities exchange, the closing price on such exchange on such day;
or (ii) if sales prices for shares of Common Stock are reported by the Nasdaq
National Market System or Small Cap Market System (or a similar system then in
use), the last reported sales price so reported on such day; or (iii) if neither
(i) nor (ii) above are applicable, and if bid and ask prices for shares of
Common Stock are reported in the over-the-counter market by Nasdaq (or, if not
so reported, by the National Quotation Bureau), the average of the high bid and
low ask prices so reported on such day. Notwithstanding the foregoing, if there
is no reported closing price, last reported sales price, or bid and ask prices,
as the case may be, for the day in question, then the current market price shall
be determined as of the latest date prior to such day for which such closing
price, last reported sales price, or bid and ask prices, as the case may be, are
available, unless such securities have not been traded on an exchange or in the
over-the-counter market for thirty (30) or more days immediately prior to the
day in question, in which case the current market price shall be determined in
good faith by, and reflected in a formal resolution of, the Board of Directors
of the Company.

         (d) Notwithstanding any provision herein to the contrary, no adjustment
in the Warrant Price shall be required unless such adjustment would require an
increase or decrease of at least one-percent (1%) in the Warrant Price;
provided, however, that any adjustments which by reason of this subsection (d)
are not required to be made shall be carried forward and taken into account in
any subsequent adjustment. All calculations under this Section 4 shall be made
to the nearest cent or the nearest one-hundredth of a share, as the case may be.



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         (e) In the event that at any time, as a result of an adjustment made
pursuant to subsection (a) above, the Holder of any Warrant thereafter exercised
shall become entitled to receive any shares of capital stock of the Company
other than shares of Common Stock, thereafter the number of such other shares so
receivable upon exercise of any Warrant shall be subject to adjustment from time
to time in a manner and on terms as nearly equivalent as practicable to the
provisions with respect to the shares of Common Stock contained in this Section
4, and the other provisions of this Warrant shall apply on like terms to any
such other shares.

         (f) If the Company merges or consolidates into or with another
corporation or entity, or if another corporation or entity merges into or with
the Company (excluding such a merger in which the Company is the surviving or
continuing corporation and which does not result in any reclassification,
conversion, exchange, or cancellation of the outstanding shares of Common
Stock), or if all or substantially all of the assets or business of the Company
are sold or transferred to another corporation, entity, or person, then, as a
condition to such consolidation, merger, or sale (a "Transaction"), lawful and
adequate provision shall be made whereby the Holder shall have the right from
and after the Transaction to receive, upon exercise of this Warrant and upon the
terms and conditions specified herein and in lieu of the shares of the Common
Stock that would have been issuable if this Warrant had been exercised
immediately before the Transaction, such shares of stock, securities, or assets
as the Holder would have owned immediately after the Transaction if the Holder
had exercised this Warrant immediately before the effective date of the
Transaction.

         (g) In case any event shall occur as to which the other provisions of
this Section 4 are not strictly applicable but the failure to make any
adjustment would not fairly protect the purchase rights represented by this
Warrant in accordance with the essential intent and principles hereof, then, in
each such case, the Company shall effect such adjustment, on a basis consistent
with the essential intent and principles established in this Section 4, as may
be necessary to preserve, without dilution, the purchase rights represented by
this Warrant.

      5. RESERVATION OF SHARES. The Company agrees at all times to reserve and
hold available out of its authorized but unissued shares of Common Stock the
number of shares of Common Stock issuable upon the full exercise of this
Warrant. The Company further covenants and agrees that all shares of Common
Stock that may be delivered upon the exercise of this Warrant will, upon
delivery, be fully paid and nonassessable and free from all taxes, liens and
charges with respect to the purchase thereof hereunder.

      6. NOTICES TO HOLDER. Upon any adjustment of the Warrant Price (or number
of shares of Common Stock purchasable upon the exercise of this Warrant)
pursuant to Section 4, the Company shall promptly thereafter cause to be given
to the Holder written notice of such adjustment. Such notice shall include the
Warrant Price (and/or the number of shares of Common Stock purchasable upon the
exercise of this Warrant) after such adjustment, and shall set forth in
reasonable detail the Company's method of calculation and the facts upon which
such calculations were based. Where appropriate, such notice shall be given in
advance and included as a part of any notice required to be given under the
other provisions of this Section 6.



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<PAGE>   6

         In the event of (a) any fixing by the Company of a record date with
respect to the holders of any class of securities of the Company for the purpose
of determining which of such holders are entitled to dividends or other
distributions, or any rights to subscribe for, purchase or otherwise acquire any
shares of capital stock of any class or any other securities or property, or to
receive any other right, (b) any capital reorganization of the Company, or
reclassification or recapitalization of the capital stock of the Company or any
transfer of all or substantially all of the assets or business of the Company
to, or consolidation or merger of the Company with or into, any other entity or
person, or (c) any voluntary or involuntary dissolution or winding up of the
Company, then and in each such event the Company will give the Holder a written
notice specifying, as the case may be (i) the record date for the purpose of
such dividend, distribution, or right, and stating the amount and character of
such dividend, distribution, or right; or (ii) the date on which any such
reorganization, reclassification, recapitalization, transfer, consolidation,
merger, conveyance, dissolution, liquidation, or winding up is to take place and
the time, if any is to be fixed, as of which the holders of record of Common
Stock (or such capital stock or securities receivable upon the exercise of this
Warrant) shall be entitled to exchange their shares of Common Stock (or such
other stock securities) for securities or other property deliverable upon such
event. Any such notice shall be given at least 10 days prior to the earliest
date therein specified.

         7. NO RIGHTS AS A STOCKHOLDER. This Warrant does not entitle the Holder
to any voting rights or other rights as a stockholder of the Company, nor to any
other rights whatsoever except the rights herein set forth.

         8. ADDITIONAL COVENANTS OF THE COMPANY. For so long as the Common Stock
is listed for trading on any regional or national securities exchange or Nasdaq
(National Market or Small Cap System), the Company shall, upon issuance of any
shares for which this Warrant is exercisable, at its expense, promptly obtain
and maintain the listing of such shares.

         The Company shall comply with the reporting requirements of Sections 13
and 15(d) of the Exchange Act for so long as and to the extent that such
requirements apply to the Company.

         The Company shall not, by amendment of its Articles or Certificate of
Incorporation or through any reorganization, transfer of assets, consolidation,
merger, dissolution, issue or sale of securities, or any other voluntary action,
avoid or seek to avoid the observance or performance of any of the terms of this
Warrant. Without limiting the generality of the foregoing, the Company (a) will
at all times reserve and keep available, solely for issuance and delivery upon
exercise of this Warrant, shares of Common Stock issuable from time to time upon
exercise of this Warrant, (b) will not increase the par value of any shares of
capital stock receivable upon exercise of this Warrant above the amount payable
therefor upon such exercise, and (c) will take all such actions as may be
necessary or appropriate in order that the Company may validly and legally issue
fully paid and nonassessable stock.

         9. SUCCESSORS AND ASSIGNS. This Agreement shall be binding upon and
inure to the benefit of the Company, the Holder and their respective successors
and permitted assigns.



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<PAGE>   7
         10. NOTICES. The Company agrees to maintain a ledger of the ownership
of this Warrant (the "Ledger"). Any notice hereunder shall be given by
registered or certified mail if to the Company, at its principal executive
office and, if to the Holder, to its address shown in the Ledger of the Company;
provided, however, that the Holder may at any time on three (3) days written
notice to the Company designate or substitute another address where notice is to
be given. Notice shall be deemed given and received after a certified or
registered letter, properly addressed with postage prepaid, is deposited in the
U.S. mail.

         11. SEVERABILITY. Every provision of this Warrant is intended to be
severable. If any term or provision hereof is illegal or invalid for any reason
whatsoever, such illegality or invalidity shall not affect the remainder of this
Warrant.

         12. GOVERNING LAW. This Warrant shall be governed by and construed in
accordance with the laws of the State of Delaware without giving effect to the
principles of choice of laws thereof.

         13. ATTORNEYS' FEES. In any action or proceeding brought to enforce any
provision of this Warrant, the prevailing party shall be entitled to recover
reasonable attorneys' fees in addition to its costs and expenses and any other
available remedy.

         14. ENTIRE AGREEMENT. This Warrant (including the Exhibits attached
hereto) constitutes the entire understanding between the Company and the Holder
with respect to the subject matter hereof, and supersedes all prior
negotiations, discussions, agreements and understandings relating to such
subject matter.

         IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
by its duly authorized officer as of the date first set forth above.


                                         PROBEX CORP.


                                         By:
                                            -----------------------------------
                                         Title:
                                               --------------------------------




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<PAGE>   8
                                    Exhibit A
                                SUBSCRIPTION FORM


(To be Executed by the Holder to Exercise the Rights To Purchase Common Stock
Evidenced by the Within Warrant)

         The undersigned hereby irrevocably subscribes for _______ shares (the
"Stock") of the Common Stock of Probex Corp. (the "Company") pursuant to and in
accordance with the terms and conditions of the attached Warrant (the
"Warrant"), and hereby makes payment of $_______ therefor by [tendering cash,
wire transferring or delivering a certified check or bank cashier's check,
payable to the order of the Company] [surrendering _______ shares of Common
Stock received upon exercise of the Warrant, which shares have a current market
price equal to such payment as required in Section 2 of the Warrant]. The
undersigned requests that a certificate for the Stock be issued in the name of
the undersigned and be delivered to the undersigned at the address stated below.
If the Stock is not all of the shares purchasable pursuant to the Warrant, the
undersigned requests that a new Warrant of like tenor for the balance of the
remaining shares purchasable thereunder be delivered to the undersigned at the
address stated below.

         In connection with the issuance of the Stock, I hereby represent to the
Company that I am acquiring the Stock for my own account for investment and not
with a view to, or for resale in connection with, a distribution of the shares
within the meaning of the Securities Act of 1933, as amended (the "Securities
Act").

         I understand that because the Stock has not been registered under the
Securities Act, I must hold such Stock indefinitely unless the Stock is
subsequently registered and qualified under the Securities Act or is exempt from
such registration and qualification. I shall make no transfer or disposition of
the Stock unless (a) such transfer or disposition can be made without
registration under the Securities Act by reason of a specific exemption from
such registration and such qualification, or (b) a registration statement has
been filed pursuant to the Securities Act and has been declared effective with
respect to such disposition. I agree that each certificate representing the
Stock delivered to me shall bear substantially the same legend as set forth on
the front page of the Warrant.

         I further agree that the Company may place stop orders on the
certificates evidencing the Stock with the transfer agent, if any, to the same
effect as the above legend. The legend and stop transfer notice referred to
above shall be removed only upon my furnishing to the Company of an opinion of
counsel (reasonably satisfactory to the Company) to the effect that such legend
may be removed.

Date:                                      Signed:
     -------------------------------              -----------------------------

                                           Address:
                                                   ----------------------------

                                                   ----------------------------


                                      A-1
<PAGE>   9
                                    Exhibit B

                                   ASSIGNMENT

    (To be Executed by the Holder to Effect Transfer of the Attached Warrant)


For Value Received __________________________ hereby sells, assigns and
transfers to _________________________ the Warrant attached hereto and the
rights represented thereby to purchase _________ shares of Common Stock in
accordance with the terms and conditions hereof, and does hereby irrevocably
constitute and appoint _________________________ as attorney to transfer such
Warrant on the books of the Company with full power of substitution.



Date:                                      Signed:
     -------------------------------              -----------------------------

Please print or typewrite                  Please insert Social Security
name and address of                        or other Tax Identification
assignee:                                  Number of Assignee:

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                                      B-1