Product review (5 stars): Worked for Whirlpool Duet purchased in 2003. (Note: NOT and OEM part)
If you ever want to feel lucky to be alive, open up your dryer.  About a year ago, the heater coil burned out on our Duet dryer (purchased in 2003).  When we opened it up, we noticed a lot of lint on the inside.  There was no question about why the heater coil burned out.  Anyway, we vacuumed out the interior and got as much of the lint as we could.  We also did a thorough cleaning of the dryer vent.  It had been about a decade since it was cleaned out.  Again, no question as to why the heater coil burned out.  I won't go into why it took us so long to clean out the dryer vent.  Lets just said we got bad info.  That was the first time we realized we were lucky that our house did not go up in flames and kill us all.  It's also the reason we don't start the dryer before going to bed or right before we leave the house.  Anyway, fast forward to last weekend.  My son came to me and said the dryer won't start.  I thought maybe the breaker flipped.  Nope.  Display was on.  When you hit start, it would click, beep, and then nothing.  No tumbling.  So my husband decided to open it up and found that the belt was broken.  We ordered the full kit instead of just the belt.  The dryer is old, so it likely needed a tuneup.  At this point, we did not see the entire inside of the dryer.  When the part came in, and my husband and I spent an hour and a half working on the dryer.  About half of that time was spent vacuuming every crevice of the inside of the dryer.  When we took out the drum, we realized how much more lint there was in there that we did not see before.  My husband pulled some off the heater coil housing that was burnt.  That is the second time I felt lucky to be alive.  The original rollers were not in bad shape.  The clips holding them in place were difficult to get off, so those were not weak.  The original rollers were not as grippy (is that a word?) as the new ones.  We went ahead and replaced those.  We probably could have gotten done sooner but we wanted to get as much lint out as possible.  We did clean out the dryer vent too, but it wasn't to bad.  It fixed our issue.  Aside from the vacuuming, the most difficult part was wrapping the belt around the gears.  It's not that it was tight or anything.  It's that you had to make sure they were wound around the gears correctly.  The drum blocks your view so you have to feel around and hope you are doing it right.  You can test it by turning the drum by hand to make sure it's winding around correctly and that there are no twists in the belt.