The back story:
This is a 90 truck, I have no idea how long its been since the AC worked. There was a teenie tiny bit of charge left in it, that I could only tell by pushing in the schrader valve to hear the hiss, it wouldn't registrar on my gauges. The compressor spins freely and doesn't make any noise (I jumper-ed it to make the clutch kick in and run a while back just to make sure it would run OK).
I'm working on doing a R12 to R134a conversion so I wanted to drain the old R12 oil out of the system. I did pull a vacuum on the system before I opened anything up just so I had some piece of mind that I didn't have a leak somewhere before I started. After seeing the system hold vacuum for a couple hours, I pulled my compressor off last night and turned it upside down and I don't even think I got a teaspoon of oil out of it. I left it sit upside down all night and I still didn't get anymore oil out if it. I also pulled my receiver dryer off (going to replace it) and it was also oil free.
So where did my oil go? Did it vaporize and slowly leave with the R12 over several years? I'm pretty positive this system hasn't ever been monkeyed with. Would you trust that compressor enough to put it back in?