1985 745t m46

this post is a follow-up on my earlier posts regarding excessive crankcase pressure in my brick.

basically I noticed a wet spot around the filler cap and have been trying to find the source of the excess crankcase pressure. First I changed the filler cap o-ring, but this solved the problem only temporarily. Next I replaced the oil separator, but the existing one wasn't clogged when I pulled it out (neither were the hoses).

After replacing the separator monday I've now driven the car for a bit (including 215 miles at 75mph) and the wet spot hasn't returned... good news, but I still want to know what the source of the problem is.

Something I've noticed is that I think the wet spot first reappeared after I drove the car and couldn't get boost. Whenever I entered the boost gauge entered the yellow I would actually get a drop in performance like the car was loosing power. The best place to run was the top of the black. The next day the problem was gone, and it has resurfaced only once (twice total in like 8 months).

I would say it might be the turbo, but I'm on my second and its only at 55k. I'm also not burning oil excessively and not blowing any smoke whatsoever (black or blue, nada).

So the short of it is I no longer believe the separator or the filler gasket played any role in this problem, and that I need to look elsewhere. I thought maybe the rings were going and I was getting blow-by (some other folks mentioned this as well), but the infrequency of this problem would seem to contradict this (wouldn't it be more frequent?).

Is it possible a bad knock sensor could be responsible? What about a bad compression bypass valve? What problem might cause intermittent excessive crankcase pressure and cause the turbo to have the performance problems indicated above? I'm moving in the direction of a relationship between the two, but really have no idea at this point.

Any help is greatly appreciated.

Thanks,
Rick

p.s. I've had the tappets adjusted and replaced the following in the last eight months, so I don't think any of them are responsible:
- exhaust manifold
- cat
- fprelay
- fpreg
- pre-pump
- fuel sender
- fuel filter
- timing belt/tensioner
- front seals
- vacuum hoses
- oil separator
- oil cap o-ring