I was reading about about oil leaks on my 1998 Audi a6. After spending a small fortune to replace the cam shaft seals and main seals and valve cover gaskets, I still had leaks. I finally replaced the breather hoses and valves on those hoses. Leaks slowed and then stopped completely. At 149.00 + shipping
I would recommend trying this first before you spend alot of money like me. Hopes this helps someone.

 

Late comer to this thread. Just thought I'd add this little tidbit about the breather hoses.
After seeing the replacement on audidiy.com, just wanted to say that the breather hoses are cake to replace. Mine were shot....totally brittle. In contrast to the audidiy author, I bought 5/8in (15.88mm) hoses, cuz that's all they had. They actually fit PERFECTLY. I recommend this size, not the 3/4in ones.