well sorry but I have seen the subie coolant treatment stop waterpump
leaks,  had it do so on my own 88 fox lasted well over 8 months. also have
seeen it work on the wbx inner o rings and clylinder gaskets , as well as  the
bigger head seal gasket ,but not as well mostly if the leak there is  massive
  later  mark d

In a message dated 2/24/2012 12:02:59 P.M. Eastern Standard Time,
d23haynes57@HOTMAIL.COM writes:

Coolant  sealers and stop leaks do not work on water pump seals as they are
a
moving  seal, not a hole to be clogged. Also once the water pump does leak
the  coolant can work into the bearing wiping it out quickly.

Also the  vanagon water boxer has absolutely nothing in common with head
gasket  design so no Subaru benefit here. Most any coolant sealer will work
on the  outer gasket as long as it not beginning to tear or split  open.

Dennis