Oil leaking around the housing were oil filter connects. Is this a gasket or what?
Probably the gasket. Did you just have an oil change done? Maybe the old gasket is still on the mating surface and you have a leak. If not, then drain the oil and replace with a new one or reinstall the old depending on how miles are on the oil.
Remember to lubricate the new oil filter gasket with oil prior to installation to insure a good seal between it and the mounting surface on the block. Then hand tighten.
I just had a similar problem. My came from the oil pressure sensor and ran down the back side of the oil filter. It was $18.
Looking for a Used A4 in your area?
CarGurus has 12,041 nationwide A4 listings starting at $950.
Search Audi A4 Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Audi A4 Experts