1999 Passat 1.8T automatic just will not run the way it use too. I believe the tension arm for the cam chain is noise and the gaskit should be replaced, but even for 120,000+ I should have a lot more power. I noticed that the tranny will drop two gears were it need to drop only one before. I've replaced my plugs, fuel filter, and air filter. Nothing. I asked my mech. if the catilitic converter might be clogged. He stated that it didn't appear so due to the lack of noise. I asked about the turbo. He states again, that it sounded fine.

I normally use high octain gas 92+
I noticed that I getting oil on the sheath under the engine.

I'd find someone who can check the cat by checking the exhaust backpressure (easiest to do through the oxygen sensor port) since they can get clogged w/o breaking up & rattling. A clogged cat usually would have made the exhaust sound different (especially at high RPM's), but it could have changed slowly & you don't notice it. It could also have a turbo problem even if it sounds fine. Verify the oil leak isn't coming from there - also look for it pumping oil into the air intake system.