are you listening around with a hose, used as a 'listening tube' ?

do that to pinpoint the leaks.
and ...
you know.........those pipes get old, sometimes crack, the ends can warp
some so the flanges are not really flat ..the two flanges on the rear pipe
may not be in the same plane anymore, etc.

I'd say there is 'an art' to fitting used exhaust pipes onto a wbxr engine
so things work well.
For example....where the front and rear pipes bolt to the flange on the J
pipe ..
it's very common to need two exhasut port gaskets  for the forward pipe, and
only one for the rear pipe at the twin or double flange.

pinpoint the leak areas and attack those spots.

'tap sound' sounds odd.
often a small leak is more like a click sound, under load and acceleration.

listen around with a hose. the one I use is about 18 inches long and 3/8ths
inch ID .
whatever you do ..
do not get any hair, clothes, or jewlery in any moving parts on the engine
!!!!!

Patience is a hallmark of being a really good van or car technician.
Sometimes it takes endless patience to finally get it right.

Scott
www.turbovans.com

----- Original Message -----
From: "Susie Ingham" <dingham605@AOL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, April 18, 2011 8:21 PM
Subject: Dang exhaust leak-- any tips?

1984 1.9L

 We had a loose bolt ( stripped threads by PO)  at the header on cylinder
number 4- Hubby learned how to Heliocoil ( sp?) it. So he has put it
together, then taken it off and  filed down the  pipes and put it back on
and each time a really loud tap sound comes from the exhaust.  we believe
it's at the exhaust pipe at   cylinder #2... are there any tips that will
help us get the leaks out? It is so frustrating !!
 thanks,
 Susie