1986 R80RT Final Drive housing??

I dropped the oil out of the final drive. When I screwed back the drain plug to the drive shaft, it was stripped. I need to re-thread or helicoil. I got the final drive house off the swing by removing the shock absorber off, removing the adjusting nut off the brake, and the four nuts connecting the final drive to the swing arm. I took it to several machinist and was told I will have to disassemble the inside, i.e. final drive nut/washer/clutch hub, etc in order for him to bring pass the drill bit down so it will not damage the inside? Is this so AND is it difficult. I do have a service manual but it is questionable for me?

Thanks

If it is the drain plug for the final drive itself, they probably want you to remove the ring gear. That's fairly straightforward although you have to make your own mind up on that.

If it's the drain for the swingarm, underneath the front of the final drive housing, that is considerably more complicated. You need to remove the threaded ring, which means taking off the nut.

Which is it?

It's right next to where the housing disconnects to the swing arm SO I would have to remove the nut so a machinist could work.

OK, well to answer your initial questions, yes it is necessary to remove those parts and yes it is on the difficult side. If you have a BMW mechanic nearby, that would be easiest since he would have the tools to remove and reinstall those parts. Of course, he could also repair the thread. For instance, if you walked into my shop, it would be 45 minutes to an hour in all. You need to find a way to hold the housing while you loosen and tighten things. Cycleworks sells a tool that will help you remove the nut, and may have one to help you remove the threaded ring.