My '89 80 Quattro (46K miles) fuel filler leaks often enough that I have
whined at the dealer, who replaced the gas cap seal. No change. It happens
most often during a drive home; home is at 8600', work is at 6000', so the
pressure differential may be my problem. However, it doesn't happen
every day; and it has happened when driving between Denver and Colo Springs
(700' difference), so I dunno. It doesn't require a full tank.
Also, parking on any kind of incline with a full tank will cause the
overflow tube (at the back of the right rear wheel well) to start dripping
gasoline. This one is easy enough to prevent, once one knows about it,
and is clearly different from a fuel filler leak.