I have a valve seal that has leaked oil into the cylinder since I bought my 1600 Duetto in 2008. I replaced them when I did the head gasket earlier this year. It started leaking, and when I removed it it was oval. Assuming that it could have been an installation error I replaced it again, with same results after a couple of hundred miles. Compression is 200 PSI across all 4 cylinders, so I'm sure it's not a ring problem. The head was refurbished just before I bought the car. I'm thinking (a sure sign of trouble) that perhaps a bad guide was replaced in that cylinder with one that requires a Teflon seal. Is there a way to tell the difference between the two types of valve guides with the head on the motor?