A major problem with the S8 needs help mechanic

Need urgent help!!!

I bought an S8 from 12/98. Which has 150,000 down. Now I have the problem that if you drive a little faster after oil stinks the reason is that I have got oil on the cat "drip" on the engine everything clean where I get to and after 3 days (about 1000 km drive) it looks like before however not much oil consumption can detect on the tarpaulin. but still bothers me out of the valve cover comes a bit but don't think that's it. A factory town told me today the head seal should it be wanted for 1500 euros. The other one told me it was just the valve lid, but I don't think so. Maybe somewhere on the oil sensor or what's sitting in the back of the engine? so it does not run oil in water or anything, even no clouds from the exhaust. Search a specialist for something like that don't like to give it to a factory town that does that for the first time search because who knows every screw on the car and not so much expensive is helping a lot too. Please help me many thanks in advance!!!!!!