Well, I found one of my vacuum leaks, at least. There is still one lurking, but this one, at the throttle boot, was almost certainly causing problems.
Here are some photos of the problem and the fix.
I'm a little concerned about the amount of oil on the breather hose. Once I find the rest of the vacuum leaks, Pod is heading into Buslab to get the oil cooler seals replaced, and I'll discuss the breather hose symptom with them.