Check coolant lines for leaking.  If the heads are leaking you will not have
to wonder about it you will know.  If all coolant lines are OK (especially
check the two on the back side of the head on the passenger side) and you
still see puddles then if you are like most Vanagon owners on this list you
can throw all kinds of money at the problem and then have it happen again in
the not too distant future.  $3000 for the installation of a new motor, $1500
for new heads on both sides and gaskets, even if both heads are only a little
pitted and you do all the work yourself you are looking at $130 for the head
gasket kit for both sides and $70 to get your heads pressure tested at a good
shop (you don't want this to happen again in another 20k miles do you?).  And
what happens if you do all this work, can I guarantee that your motor will
never have this problem again or that it will not have this problem for a
long time to come?  No.  I have heard of guys with 10k on the brand new motor
and have the head gaskets go.  What is the solution?  Ever thought of putting
in a Chevy V6?  More power, more reliability, and you could buy the kit and a
rebuilt engine and have it installed for under $2000 and never have to
realistically worry about the head gasket problem again.  Thats the only
cure.  I hope I helped ya.
Ken Wilford   John 3:16
P.S. My heads just went this week so I can sympathize.