So today I picked up my new ride: a 1985 R80RT. I stopped by my house to pick up some more suitable attire, and when I come back out to ride it some more... oil everywhere. There's at least ~100ML of it all over the driveway under the bike, leaking from the "shelf" at the back of the oil pan. My first thought was rear main seal, but... when I first test rode it, there was a little oil coming out of the airbox due to a split line. The owner (mechanic friend of mine) replaced it, and it stopped leaking. Now it's spewing even more out, however the oil that's in the crankcase is clean and clear looking, while the oil that's on the ground is black (not gear oil) and filthy. This makes me think that it's something to do with the crankcase breather/venting maybe spewing oil out from wherever it is and it trickling down behind the flywheel. There's also a lot of blowby if I run it without the dipstick inserted, however it doesn't smoke even when cold and runs very well - it also has very low mileage, at about 20K. I won't have my shop manual in until next week - can someone advise me on how to get to the breather, or possibly anything else I should check? Maybe an exploded diagram?