Oil in the cylinder

[Marc Zeitlin]

My engine a Lycoming 320 used a liter of oil in the last two hours...
Puzzled, how did the oil get past the rings if the compression is normal?

First guess - broken oil rings. I had two a customer and a hangar mate have broken oil rings in their O-235 and O-360 Lycoming within a couple of weeks of one another - very strange. Lycoming said that it's not common, but it does happen. The first sign on the O-360 was huge power loss and vibration - on the O-235, it was using 4 quarts of oil in an hour and a half.

Could a valve guide seal leak that much??

I'm not an engine expert, but that seems unlikely - I think you'd see other symptoms before that if the guide was that loose.