OK, mea culpa - here''s where I get to eat humble pie.
It can go both ways. In fact, I have seen it go both ways, and don''t know what I was thinking. It will most often go the way that Phil describes, and Chevy II thought, that is, transmission to engine, but that depends on the deterioration of the freewheel seal, and other lab seals in the system. In my defense, I will only say that I wrote that at 9:15 PM forum time, which is 10:15 PM real time, and both are waaaaaaaaay past my bedtime. I had consumed waaaaay too much red wine and shouldn''t have been allowed near any form of public media.
On with it, then.
Chevy - the reason has nothing to do with oil pressure, as both cavities are vented to atmosphere, therefore, very little pressure exists in them. The engine gearbox actually contains very little oil when running, as it primarily a series of jets, and the oil is taken back into the system through the sump. The transmission, on the other hand, contains most of its oil in the case itself, and pumps oil to the freewheel (albeit at a trickle), but therefore will be more likely to give up its oil to the engine.
Hope that clears things up.
