Oil leak under instake manifold - Can the vacuum tree leak oil?
 

I have an oil leak under my intake manifold. It appears to be coming from the vacuum tree. I thought this was a vacuum line that did not carry oil. There is a small pool of oil in this area (attached a modified txblake image). Is it possible for it to come from the vacuum tree? It is connected to the AOS. It is dry near the plug wires so the cam housing seal is not leaking. Also, the balance shaft seal was replaced and it looks dry around there. It is wet under the intake manifold. I cannot think of any other place this oil is coming from. I would like to see what I might need to order before removing the intake manifold. Inside the intercooler lines are coated with oil, but not dripping. The MAF is also dry inside. Turbo has no shaft play. 112,000 miles on the car (86 Turbo). Oil consumption is minimal. I never need to top off between oil changes.

Whats this I read about removing the downpipe to replace o-rings in the AOS? Would I really have to do that if that is the problem?

I can't imagine that you could get enough oil through the AOS return to pool on top of the motor without the tree pipe also being full of oil. Oil vapors - sure, but not enough to pool, especially if you aren't consuming any oil between changes. An oil film inside of the IC and pipes is typical and shouldn't cause alarm.

I would look closer at things that have pressurized oil near the pool like the upper balance shaft housing seal (not the front shaft seal) or the housing itself. You might also look closely at the turbo oil supply line, although I'd think your turbo housing would be coated with oil if that was failing.

As for re-sealing the AOS, yes, the turbo/down pipe needs to come out. It's really tight in there... if you go that far, don't forget to replace the turbo oil drain vent to AOS hose while you're in there.