My 89 420SEL just had this problem.
I went to Home Depot and bought some nylon table/chair leg ends, some countersink type hex key bolts (#10 - 32 x 1"), nuts (3/8" flat and self-locking), and washers. Drilled out the nylon leg end and removed the nail, countersunk with a larger bit and sunk the bolt through it until the head was flush with the surface, then nutted it down tight. Next, I added a few washers as a spacer.
Used a Dremel to grind off the flat side of the stud from the guide, then attached my new assembly. Another washer and a self-locking nut complete the new installation.
Greased up the gear teeth, the slider, and the guide, and installed it. Total time (not counting the trip to the store) about 20 minutes. Total cost, including a can of marine wheel bearing grease, just over $25, and I have enough pieces to do all 8 windows on 2 cars.
Not sure how everyone else does it, but in removing the window motor, I found it easiest to de-pin the switch plug (took a picture of the wire arrangement with my cellphone camera - Ain't technology great?) and remove it all as an assembly. (Had to disconnect the glass guide. No big deal, unless you don't!)
I expect in another 20 years, it might need replacing again.