One of the first things I had to do. Bought a repair kit off Ebay from an outfit in the Land Down under... about $32. I dont know if MBZ offers a version or not.
This kit included two rollers (hard, white, nylon sorta material), a couple allen head cap screws (shouldered for the lenght of the rollers), and a couply nyloc nuts.
The procedure (included in the kit) is to drill out the swedged or coined end of the existing pin, usually from the bottom, though on my car one side was located on top while the other side required drilling from the bottom. Be carful not to enlarge the hole too much. Drive out the old pin and remove the old roller... or whats left of it.
Insert the new roller in the bracket. Insert the cap screw and tighten the nut snugly. The shouldered cap screw prevent binding of the roller if you too aggressive with the wrench.
It was helpful to first remove the guide arm from the quarter panel door jamb... allows the door to more fully open giving you the needed room to get a drill and bit in true vertical position. Also a good idea to dab some paint or heavy grease on any metal exposed during drilling... fight the rust demon.
Took about 1-1/2 hours, and man was it worth it... the doors now have a real quality feel when opening and closing.
My 2 cents...
`68 280sl
`62 Lincoln Continental Conv.
`73 450sl