Advice: you don't need to be at 4,000 RPM. Just a guess, but I never exceed 3,000, so I'm just imagining the whine it must make.

The shaft nearest the head, as you are facing the engine, is a silent shaft, and it is run by its own timing belt. Did the timing belt on it break? Might explain some of the problem.

Oil in the intake sounds to me like jet valve problems.

If the engine isn't running at all, I'd suggest you dismantle it enough to remove the cylinder head. That will let you see what's going on in there.