<PAGE>

                                                                   EXHIBIT 10.23

[COMERICA LOGO]

                                    GUARANTY

As of June 6, 2003, the undersigned, for value received, unconditionally and
absolutely guarantee to Comerica Bank ("Bank"), a Michigan banking corporation,
payment when due, whether by stated maturity, demand, acceleration or otherwise,
of all existing and future indebtedness ("Indebtedness") to the Bank of
Renaissance Alliance Insurance Services, LLC, a Massachusetts limited liability
company ("Borrower"). Indebtedness includes without limit any and all
obligations or liabilities of the Borrower to the Bank, whether absolute or
contingent, direct or indirect, voluntary or involuntary, liquidated or
unliquidated, joint or several, known or unknown; any and all indebtedness,
obligations or liabilities for which Borrower would otherwise be liable to the
Bank were it not for the invalidity, irregularity or unenforceability of them by
reason of any bankruptcy, insolvency or other law or order of any kind, or for
any other reason; any and all amendments, modifications, renewals and/or
extensions of any of the above; and all costs of collecting Indebtedness,
including, without limit, attorney fees. Any reference in this Guaranty to
attorney fees shall be deemed a reference to reasonable fees, charges, costs and
expenses of both in-house and outside counsel and paralegals, whether or not a
suit or action is instituted, and to court costs if a suit or action is
instituted, and whether attorney fees or court costs are incurred at the trial
court level, on appeal, in a bankruptcy, administrative or probate proceeding or
otherwise. All costs shall be payable immediately by the undersigned when
incurred by the Bank, without demand, and until paid shall bear interest at the
highest per annum rate applicable to any of the Indebtedness, but not in excess
of the maximum rate permitted by law.

1.   LIMITATION: The total obligation of the undersigned under this Guaranty is
     UNLIMITED unless specifically limited in the Additional Provisions of this
     Guaranty, and this obligation (whether unlimited or limited to the extent
     specified in the Additional Provisions) shall include, IN ADDITION TO any
     limited amount of principal guaranteed, all interest on that limited
     amount, and all costs incurred by the Bank in collection efforts against
     the Borrower and/or the undersigned or otherwise incurred by the Bank in
     any way relating to the Indebtedness, or this Guaranty, including without
     limit attorney fees. The undersigned agree(s) that (a) this limitation
     shall not be a limitation on the amount of Borrower's Indebtedness to the
     Bank; (b) any payments by the undersigned shall not reduce the maximum
     liability of the undersigned under this Guaranty unless written notice to
     that effect is actually received by the Bank at, or prior to, the time of
     the payment; and (c) the liability of the undersigned to the Bank shall at
     all times be deemed to be the aggregate liability of the undersigned under
     this Guaranty and any other guaranties previously or subsequently given to
     the Bank by the undersigned and not expressly revoked, modified or
     invalidated in writing.

2.   NATURE OF GUARANTY: This is a continuing Guaranty of payment and not of
     collection and remains effective whether the Indebtedness is from time to
     time reduced and later increased or entirely extinguished and later
     reincurred. The undersigned deliver this Guaranty based solely on the
     undersigned's independent investigation of (or decision not to investigate)
     the financial condition of Borrower and are not relying on any information
     furnished by the Bank. The undersigned assume full responsibility for
     obtaining any further information concerning the Borrower's financial
     condition, the status of the Indebtedness or any other matter which the
     undersigned may deem necessary or appropriate now or later. The undersigned
     knowingly accept the full range of risk encompassed in this Guaranty, which
     risk includes, without limit, the possibility that Borrower may incur
     Indebtedness to the Bank after the financial condition of the Borrower, or
     the Borrower's ability to pay debts as they mature, has deteriorated.

3.   APPLICATION OF PAYMENTS: The undersigned authorize the Bank, either before
     or after termination of this Guaranty, without notice to or demand on the
     undersigned and without affecting the undersigned's liability under this
     Guaranty, from time to time to: (a) apply any security and direct the order
     or manner of sale; and (b) apply payments received by the Bank from the
     Borrower to any indebtedness of the Borrower to the Bank, in such order as
     the Bank shall determine in its sole discretion, whether or not this
     indebtedness is covered by this Guaranty, and the undersigned waive any
     provision of law regarding application of

<PAGE>

     payments which specifies otherwise. The undersigned agree to provide to the
     Bank copies of the undersigned's financial statements upon request.

4.   SECURITY: The undersigned grant to the Bank a security interest in and the
     right of setoff (which shall only be exercisable upon the occurrence and
     during the continuance of an Event of Default on the Indebtedness) as to
     any and all property of the undersigned now or later in the possession of
     the Bank. The undersigned further assign to the Bank as collateral for the
     obligations of the undersigned under this Guaranty all claims of any nature
     that the undersigned now or later have against the Borrower (other than any
     claim under a deed of trust or mortgage covering California real property)
     with full right on the part of the Bank, in its own name or in the name of
     the undersigned, to collect and enforce these claims. The undersigned agree
     that no security now or later held by the Bank for the payment of any
     Indebtedness, whether from the Borrower, any guarantor, or otherwise, and
     whether in the nature of a security interest, pledge, lien, assignment,
     setoff, suretyship, guaranty, indemnity, insurance or otherwise, shall
     affect in any manner the unconditional obligation of the undersigned under
     this Guaranty, and the Bank, in its sole discretion, without notice to the
     undersigned, may release, exchange, enforce and otherwise deal with any
     security without affecting in any manner the unconditional obligation of
     the undersigned under this Guaranty. The undersigned acknowledge and agree
     that the Bank has no obligation to acquire or perfect any lien on or
     security interest in any asset(s), whether realty or personalty, to secure
     payment of the Indebtedness, and the undersigned are not relying upon any
     asset(s) in which the Bank has or may have a lien or security interest for
     payment of the Indebtedness.

5.   OTHER GUARANTORS: If any Indebtedness is guaranteed by two or more
     guarantors, the obligation of the undersigned shall be several and also
     joint, each with all and also each with any one or more of the others, and
     may be enforced at the option of the Bank against each severally, any two
     or more jointly, or some severally and some jointly. The Bank, in its sole
     discretion, may release any one or more of the guarantors for any
     consideration which it deems adequate, and may fail or elect not to prove a
     claim against the estate of any bankrupt, insolvent, incompetent or
     deceased guarantor; and after that, without notice to any guarantor, the
     Bank may extend or renew any or all Indebtedness and may permit the
     Borrower to incur additional Indebtedness, without affecting in any manner
     the unconditional obligation of the remaining guarantors. The undersigned
     acknowledge that the effectiveness of this Guaranty is not conditioned on
     any or all of the indebtedness being guaranteed by anyone else.

6.   TERMINATION: Any of the undersigned may terminate their obligation under
     this Guaranty as to future Indebtedness (except as provided below) by (and
     only by) delivering written notice of termination to an officer of the Bank
     and receiving from an officer of the Bank written acknowledgment of
     delivery; provided, however, the termination shall not be effective until
     the opening of business on the fifth (5th) day ("effective date") following
     written acknowledgment of delivery. Any termination shall not affect in any
     way the unconditional obligations of the remaining guarantors, whether or
     not the termination is known to the remaining guarantors. Any termination
     shall not affect in any way the unconditional obligations of the
     terminating guarantors as to any Indebtedness existing at the effective
     date of termination or any Indebtedness created after that pursuant to any
     commitment or agreement of the Bank or pursuant to any Borrower loan with
     the Bank existing at the effective date of termination (whether advances or
     readvances by the Bank after the effective date of termination are optional
     or obligatory), or any modifications, extensions or renewals of any of this
     Indebtedness, whether in whole or in part, and as to all of this
     Indebtedness and modifications, extensions or renewals of it, this Guaranty
     shall continue effective until the same shall have been fully paid. The
     Bank has no duty to give notice of termination by any guarantors to any
     remaining guarantors. The undersigned shall indemnify the Bank against all
     claims, damages, costs and expenses, including, without limit, reasonable
     attorney fees, incurred by the Bank in connection with any suit, claim or
     action against the Bank arising out of any modification or termination of a
     Borrower loan or any refusal by the Bank to extend additional credit in
     connection with the termination of this Guaranty.

                                      -2-

<PAGE>

7.   REINSTATEMENT: Notwithstanding any prior revocation, termination, surrender
     or discharge of this Guaranty (or of any lien, pledge or security interest
     securing this Guaranty) in whole or in part, the effectiveness of this
     Guaranty, and of all liens, pledges and security interests securing this
     Guaranty, shall automatically continue or be reinstated in the event that
     any payment received or credit given by the Bank in respect of the
     Indebtedness is returned, disgorged or rescinded under any applicable state
     or federal law, including, without limitation, laws pertaining to
     bankruptcy or insolvency, in which case this Guaranty, and all liens,
     pledges and security interests securing this Guaranty, shall be enforceable
     against the undersigned as if the returned, disgorged or rescinded payment
     or credit had not been received or given by the Bank, and whether or not
     the Bank relied upon this payment or credit or changed its position as a
     consequence of it. In the event of continuation or reinstatement of this
     Guaranty and the liens, pledges and security interests securing it, the
     undersigned agree upon demand by the Bank, to execute and deliver to the
     Bank those documents which the Bank determines are appropriate to further
     evidence (in the public records or otherwise) this continuation or
     reinstatement, although the failure of the undersigned to do so shall not
     affect in any way the reinstatement or continuation. If the undersigned do
     not execute and deliver to the Bank upon demand such documents, the Bank
     and each Bank officer is irrevocably appointed (which appointment is
     coupled with an interest) the true and lawful attorney of the undersigned
     (with full power of substitution) to execute and deliver such documents in
     the name and on behalf of the undersigned.

8.   WAIVERS: The undersigned , to the extent not expressly prohibited by
     applicable law, waive any right to require the Bank to: (a) proceed against
     any person or property; (b) give notice of the terms, time and place of any
     public or private sale of personal property security held from the Borrower
     or any other person, or otherwise comply with the provisions of Sections
     9-611 or 9-621 of the Michigan or other applicable Uniform Commercial Code,
     as the same may be amended, revised or replaced from time to time; or (c)
     pursue any other remedy in the Bank's power. The undersigned waive notice
     of acceptance of this Guaranty and presentment, demand, protest, notice of
     protest, dishonor, notice of dishonor, notice of default, notice of intent
     to accelerate or demand payment of any Indebtedness, any and all other
     notices to which the undersigned might otherwise be entitled, and diligence
     in collecting any Indebtedness, and agree that the Bank may, once or any
     number of times, modify the terms of any Indebtedness, compromise, extend,
     increase, accelerate, renew or forbear to enforce payment of any or all
     Indebtedness, or permit the Borrower to incur additional Indebtedness, all
     without notice to the undersigned and without affecting in any manner the
     unconditional obligation of the undersigned under this Guaranty.

     The undersigned unconditionally and irrevocably waive each and every
     defense and setoff of any nature which, under principles of guaranty or
     otherwise, would operate to impair or diminish in any way the obligation of
     the undersigned under this Guaranty, and acknowledge that each such waiver
     is by this reference incorporated into each security agreement, collateral
     assignment, pledge and/or other document from the undersigned now or later
     securing this Guaranty and/or the Indebtedness, and acknowledge that as of
     the date of this Guaranty no such defense or setoff exists.

9.   WAIVER OF SUBROGATION: The undersigned waive any and all rights (whether by
     subrogation, indemnity, reimbursement, or otherwise) to recover from the
     Borrower any amounts paid by the undersigned pursuant to this Guaranty.

10.  SALE/ASSIGNMENT: The undersigned acknowledge that the Bank has the right to
     sell, assign, transfer, negotiate, or grant participations in all or any
     part of the Indebtedness and any related obligations, including, without
     limit, this Guaranty, without notice to the undersigned and that the Bank
     may disclose any documents and information which the Bank now has or later
     acquires relating to the undersigned or to the Borrower in connection with
     such sale, assignment, transfer, negotiation, or grant. The undersigned
     agree that the Bank may provide information relating to this Guaranty or
     relating to the undersigned to the Bank's parent, affiliates, subsidiaries
     and service providers.

                                      -3-

<PAGE>

11.  GENERAL: This Guaranty constitutes the entire agreement of the undersigned
     and the Bank with respect to the subject matter of this Guaranty. No
     waiver, consent, modification or change of the terms of the Guaranty shall
     bind any of the undersigned or the Bank unless in writing and signed by the
     waiving party or an authorized officer of the waiving party, and then this
     waiver, consent, modification or change shall be effective only in the
     specific instance and for the specific purpose given. This Guaranty shall
     inure to the benefit of the Bank and its successors and assigns and shall
     be binding on the undersigned and the undersigned's heirs, legal
     representatives, successors and assigns including, without limit, any
     debtor in possession or trustee in bankruptcy for any of the undersigned.
     The undersigned have knowingly and voluntarily entered into this Guaranty
     in good faith for the purpose of inducing the Bank to extend credit or make
     other financial accommodations to the Borrower. If any provision of this
     Guaranty is unenforceable in whole or in part for any reason, the remaining
     provisions shall continue to be effective. THIS GUARANTY SHALL BE GOVERNED
     BY AND CONSTRUED IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE OF
     MICHIGAN, WITHOUT REGARD TO CONFLICT OF LAWS PRINCIPLES.

12.  HEADINGS: Headings in this Agreement are included for the convenience of
     reference only and shall not constitute a part of this Agreement for any
     purpose.

13.  ADDITIONAL PROVISIONS: None.

14.  JURY TRIAL WAIVER: THE UNDERSIGNED AND BANK ACKNOWLEDGE THAT THE RIGHT TO
     TRIAL BY JURY IS A CONSTITUTIONAL ONE, BUT THAT IT MAY BE WAIVED. EACH
     PARTY, AFTER CONSULTING (OR HAVING HAD THE OPPORTUNITY TO CONSULT) WITH
     COUNSEL OF THEIR CHOICE, KNOWINGLY AND VOLUNTARILY, AND FOR THEIR MUTUAL
     BENEFIT WAIVES ANY RIGHT TO TRIAL BY JURY IN THE EVENT OF LITIGATION
     REGARDING THE PERFORMANCE OR ENFORCEMENT OF, OR IN ANY WAY RELATED TO, THIS
     GUARANTY OR THE INDEBTEDNESS.

                                      -4-

<PAGE>

IN WITNESS WHEREOF, Guarantors have signed and delivered this Guaranty the day
and year first written above.

                                        ________________________________________
                                        J. BRUCE COCHRANE

                                        MEADOWBROOK INSURANCE GROUP, INC.

                                        By:_____________________________________

                                        Its:____________________________________

                                        RENAISSANCE INSURANCE AGENCY, INC.

                                        By:_____________________________________

                                        Its:____________________________________

                                        COCHRANE & PORTER INSURANCE AGENCY, INC.

                                        By:_____________________________________

                                        Its:____________________________________

                                      -5-