I'm losing oil between changes. The car probably uses a quart in 1500 or 2000 miles. There are small leaks from the oil filler cap and also the breather where it leaves the head (visible w/ "20V" cover removed). No other places are leaking from what I can tell after a few up close inspections. I went to replace the flame trap, and this car doesn't have one. The new one fits in the holder but I read that this is correct for some 98's and I left it out pending resolution of the vacuum pressure issue. The O ring is 7K miles old and the throttle body is clean. I cleaned out the housing for the trap and its inlets that the hoses connect to. The small inlet was pretty clogged. The larger inlet also benefitted from the cleaning. I checked both hoses for cloggage and both have flow with air. The large hose will move air back through the removed oil filler cap at a healthy rate.

After doing this and re-asembly I expected negative pressure/vacuum with a removed oil filler cap. This is barely noticable at idle. At 3000 RPM and a warm engine there is outward pressure at the oil cap, confirmed both with the cap in place and removing it.

Any suggestions on what to try next? Is the cannister under the intake manifolds just filling with oil from this pressure? Does that oil make it back to the pan?

The car has 75K miles, was built early (5/97 Euro delivery) and was changed over to synthetic oil at 67K. It's foaming on its dipstick as a few others' cars are too.

Thanks for your help and suggestions.