Well, I'm trying to bring an '89 ebay special back to life.  Had sort of an interesting experience the other day.  

I've checked the oil on the bike several times, when it was both cold and warm.  I even added some to bring it up when I first got the bike.  The level was right at the top of the mark on the dip stick.  The bike has an uncertain maintanence history and likely hasn't run in years.

I had a leak in a gas line a couple days ago, and the old brittle lines were replaced.  Gas likely covered the engine case, but the oil looked un-tainted and smelled normal.  

I was out riding it a day or two later and it started running like crap.  Could barely get it back to the house.  When I parked in the driveway, I noticed oil dripping out of the tail pipe!!!!  

I put it on the center stand and pulled out the dip stick.  The oil level was about an inch and a half over the "full" mark on the dip stick.

I drained it out and there was no gas "floating" on the old oil in the drain pan.  The oil that came out was black as death.

Is it possible that oil was trapped in an oil galley, and came un-clogged and drained into the engine case?  What the hell was that all about?  There was way too much oil in there!!!  Where did it all come from?

I don't know where the extra oil came from and I don't know if too much oil will make it come out of the pipe...but did you check your air filter?  It's proly got a little puddle of oil in there too.  One would think that oil anywhere near the exhaust would mean excessive wear on the cylinders/pistons/rings.  I would do a compression test.