No miracle cure in this post... just some common problems and a 
little bit of life extending hope.

As we all unfortunately know, the wasserboxer exhaust is prone to 
cracking, if the rust doesn't get it first.  3 areas i've had repaired 
successfully are:

1. crack in header pipe just at the flange that bolts to the exhaust 
port

2.  crack in header pipe at "Y" junctions

3.  crack in header pipe at front support bracket (present only from 
'86 on)

note:  these cracks were on 3 different vanagons so i wasn't 
inflicted with all this pain on one vehicle...

in each case, the local muffler shops were able to wire-feed 
weld the cracks solid again.  the repair i just had done on the '87 
(a #3 type crack) was done by cutting out the cracked section and 
welding in a new piece of pipe.  this guy's work was pure art.  he 
was good.  $35 and fixed while-u-wait :)

anyway, if most of the exhaust is solid, these crack repairs can get 
you a few more years farther from the inevitable :(  so far, these 
cracks are occuring in areas with relatively solid pipe left.

oh, i've tried the JB Weld stuff too, it just can't stand the heat.

so, don't despair completely-- weld 'dem cracks

-dan