gas in oil

I just checked my oil on my a4 quattro 1.8t and it has a small gas smell to it (not a heavy sent just a hint) I had a asked a guy at Supper Lube (dont get my oil changed there it is just down the street) and he said that I had a leaking "final drive" What the heck is that Please any help will work. Thank you all.

finaly understand final drive has nothing to do with gas in oil so I guess I now have two questions gas in oil and leaking final drive thank you for your time.