Get all the old parts that they supposedly replaced.  If they are honest they
will have already have given you the parts.  Don't try to look at the parts
on your car because they could have been spray painted.  If they can't
produce the old parts because they said that they threw them away, then ask
to see the reciepts from the parts house were they bought all this new stuff.
 If you didn't ask for the battery I can't see how they can make you pay for
it.  The spark plug/ oil drain plug is a bad sign.  After all this is over I
suggest you find another garage.  Vanagons can be costly enough to operate
without a crooked shop trying to rook you (which is what this smells like to
me and I've been had before so don't feel alone).
I am going to try some Moroso Ceramic block sealer on my leaking heads. I'll
let know how it turns out.
Yours truely
Ken Wilford   John 3:16