Originally Posted by chasbmw
if the starter only gives problems when it is under load, then ther problem is often due to wear in the bushings, this allows the armature to cock sideways under load and everything starts to go really slow.
I dont know if the bushs are available for these old 8 tooth Boschs, but given that you can buy either Valeo or Nippon Denso 8 tooth starter motors nowadays I would go for replacement.
The bushings are available several places. Motorad Electrik comes to mind.
The only part that I think I see reports about not being able to buy is the early 8 tooth pinion. These reports are rather universal however I'm not really sure that there isn't some obscure source, it's a Bosch part after all, or there isn't some way to make do, adapt, another 8 tooth pinion to the Bosch starter Armature.
If you need the 8 tooth pinion it doesn't look hopeful.