I don't know the history of my 1978 R100/7, but I suspect it has the original starter. The starter was getting weak, so--after confirming the battery and wiring were OK--I disassembled the starter. I found that the starter needed (at least) new bushings, a good cleaning and a bit of lube.
I also found the remnants of a large white plastic-like washer in the area of the drive housing/starter gear (about 35 mm OD, 25 mm ID).
What the heck is that? Where did it come from? Where can you buy this part? Thanks.