from interior ventilation it sometimes smells of gasoline

Hey guys, first of all: with my `94 B4 Avant it smells like gasoline sometimes when I turn on the interior ventilation. Even if no running car is standing in front of me or when driving free. But is not always the case. In the workshop I was told that everything in the engine room was tight, the filters changed! Hmmm? As I said, doesn’t always occur, but more and more often 😉 Second: Timing belt changes in my model are there 300,-Euro incl. material and working time appropriate? G made! thirdly: how much is the average consumption with you? I find it swallows quite a lot! How far do you get with a tank filling approx? Thank you already in advance, dears, your Nicki