Excessive oil consumption & #1 Cyl burning oil

[Schocki]

Hi Gang,
My 1991 944S2 developed a problem over the last weeks. It has 156000 km's on it and never used any oil until the cam chain tensioner failed one morning. I got the cylinder head removed from the engine, checked and all new seals (including valve stem seals) installed. Since then (at 138000 km) the car uses oil, the amount depends on the driving style. Highway uses a lot more than city cycle (about 1 qrt per 200 miles!!!) That is way too much!
But here is the problem: The car NEVER smokes on startup and I never see any smoke in the mirror, unless you push it above 5000 RPM. The gas mileage is great (30+ MpG on the Highway) and the engine runs extremely strong. However, if you pull the spark plugs they are all fine except Cyl #1 is always black and the threat is oily. There is also always some oil visible on top of the piston. I installed new valve stem seals last weekend but it did not change anything.
I will bring the car to my mechanic tomorrow and he will start to do all the checks (compression/leak down) to figure out what's wrong. He thought that the crankase ventilation could be faulty and that is the reason for the oil consumption. What about the oil separator? Could it be that it doesn't work properly and the engine is burning oil instead of oil vapors?
Anybody of you ever had such a problem? Especially at such a low mileage (99000 Miles).
Any advices or thoughts welcome!!!

Michael