Thank you for your replies, Dave Kautz, Dan Houg, Bob Hoover, Tom
Carrington, and David Schwarze!

The problem was exhaust leaks between a few flanges, even though (or
rather: because?) I had installed new gaskets. Curing the problem with
Permatex 3H wouldn't have been a good idea according to the replies since
it would either have burned away or otherwise have made life difficult
next time I wanna take the system apart. Bob also pointed out that:

"VW exhaust gaskets are normally meant to form a seal under high
temperatures, using a metal having a radically different thermal
coefficient than the metal on one side.  Using Permatex or other compounds
was common on water cooled engines that had cast iron on both sides of the
gasket.  If the manufacturer does not specify a sealant, and VW does not,
then its best not to use one."

Dan, however, suggested: "what permatex is REALLY good for is coating the
insides of pipes that slip inside each other (exhaust pipes).  something
about the permatex hangs on a allows easy disassembly."

The cure for the leak between the flanges, as suggested by Bob, is to
remove/smooth out the uneven rust erosion on the flanges. A wire wheel on
a 10,000 rpm grinder and a few blows with a hammer took care of that. 

-- 
Sami ('75 Westf.)
dakhlia@wuecona.wustl.edu
http://wuecon.wustl.edu/~samid/