I recently bought a 1973 R60/5 Hack. It is in very good condition but has a few issues I willbe dealing with. The most important are the oil leaks ... slight leaks from left side pushrod tubes but more importantly (see picture below) I have a leak from just above the oil pan in rear of case. The hole is perfectly round and smoothe, no threads. I have talked to BMW dealer and we looked at a /5 he had and there is NO HOLE. I have a buddy in MD with a R75 that has same hole with a grey plug in it! I'm not sure what the hole is here for OR why some have the hole and some do not. I was planning on dropping the pan during cleanup and thought maybe I'll just tap it and thread a bolt into the hole ...

Anybody know why this hole exists? What's it for and why do some have and others do not have it?

Thanks for any help, I'm sure I'll be asking plenty of questions in near future!