Had a very interesting experiment (totally unplanned).  I have some external
cracks in the external part of the water jacket on my boxer.  I had green
antifreeze initially.  Added some stop leak.  The leak stopped.  Later on, I
changed to the green antifreeze (phosphate free).  Within a short time, the
leak started up again.  Had to take the van in to the mechanic for some work
and he noticed that the coolent was down so he filled it up with the green
stuff.  When I got the van back, I expected to be putting coolent in it
again.  No such luck.  It stopped leaking again???  Later on, as the coolent
was used, I started adding in the orange again.  All of a sudden, the leak
was back.  Kept putting the orange antifreeze in until I ran out.  Couldn't
find a source for a while so started using the green in the mean time.
Suprise.  The leak has almost stopped again.  Normally I wouldn't think much
of this but the boxer was really leaking and now it is almost dry.  I had to
go back and review my records to make sure but this was the sequence of
events.  Very weird but in the event of an emergency, this might be a life
saver (or boxer saver as the case may be).  Seems that a lot of the stop
leaks were made before the orange antifreeze came out and there might be
something that just doesn't work right with the orange antifreeze.  For the
time being, I am still using the green even though I just found another
source for the orange antifreeze.

William