Huge Amounts of Oil Blowing out of Exhaust. Any Ideas?

[red560SL]

My 1987 560SL has been running perfectly without even a drop of oil consumption. I don't drive it much, but I do take it out for a spin at least once per month. Today was a real bummer for me. Here's what happened.

I started the engine while the vehicle was in the garage. She started up on 1st fire as it always has. I let it warm up a little before I pulled it out in the driveway. I let it keep running and warm up while I got out and started to sweep the garage floor. After about 7 minutes of running, all of a sudden out of nowhere a huge amount of black smoke pored out of the exhaust. Then a huge cloud filled the garage within moments. I rushed to the car and shut her down. I let it cool down a bit (not that it was hot). I then restarted her and smoke was everywhere. The engine itself sounds just fine. No starnge noises or anything like that. I backed her into the garage and shut her down. When I did, I noticed at least a quart of oil had spilled out on the driveway. I got out my jack and lifted the car to see if I could see where it was all coming from. What I found was oil leaking right out of the exhaust pipe where the left and right exhaust pipes collect into one.

Does anyone know what could cause this abrupt oil blow? I've ruled out things like a head gasket as they just don't fail out of nowhere and specially not as severe as this and I would have probably found coolant. It was just sitting there idling! The week before I drove it around without any problems at all. It just doesn't make sense to me. Could it be some kind of vacuum problem that may suck oil in like that? I did notice the engine reving on it's own when this happened, but nothing more than that. I am stumped!

Any clues on where to start looking would be appreciated.

Thanks,
Tony