old audi / synthetic oil question...

[ricematthews]

Synthetics can cause hardening of older seals - but this is really due to
the material used to make the seals, not the age.  I believe this is the
case for seals made before about 1980 or 82.  The only other reason that
synthetic might cause leaking is that it flows better and would probably
find a flaw in a weak and tired seal more easily.  Such a leak would likely
go away if you switched back to conventional.
-Mark