Hello Raimund,

I believe that you are talking about where the input shaft
comes out of the bellhousing?  The only reason why it
should leak there is if the seal is bad.  Since you have
already replaced the seal I would suspect the 'slinger'
portion just behind the seal may be bad as well, however,
it is rare for that to be bad unless the input shaft has
wallowed about and impacted on the sides.  If that portion
of the bellhousing is bad then you will have to replace the
entire housing as the slinger portion is not available
separately.  It is a very easy thing to replace once the
engine is out of the way ;) but is very expensive to purchase
new.  (Here in the States its about $600? or so from VW)
Perhaps you have access to wrecking yards over there
and can find a good housing much cheaper than new.

-Todd Hill
 VolksWerks Transaxles
 Olympia, WA