I opened up my dead starter with the great OM617 starter rebuild instructions in hand, to discover that the two are not very similar. The one from my 300SDL had a complex and crappy plastic reduction gear setup, which I couldn't find a kit for. The local alternator/starter guy said that parts for it were more than a new one, so he sold me a new one for $100. cash.
Since I took pictures thinking I'd rebuild, I thought it would be interesting for people to see them.
When I got the brushes end out of the housing, the brushes were a crumbled mess, floating around the armature. It all comes apart in a similar way to the OM617 starter, until you get to the splines on the end of the armature.
Here's the gear on the end of the armature, just pulled out of the housing that it inserted into.
When I took the metal plate off, it looked like this inside. You can see in the center where the splines went. That's a shattered plastic ring with gear teeth between the reduction gear setup and the starter housing.
Here's the same part with the shattered ring cleaned out.
Here's what the ring's pieces looked like.
Here's the part cleaned up a bit. The thin plastic covering shown here clamps on top of a metal housing holding the three reduction gears. Behind this presumably is the bendix gear/spring that engages the flywheel.
Not as useful as a rebuild tutorial, but kind of interesting.