The other obvious thing is to check for puddles of coolant.  If they
flushed it, they probably removed the hose going into the radiator
under the front bumper.  Maybe the clamp is loose.  The other thing is
checking the bleeder bolt in the engine compartment, if that is open,
then it'll seep coolant when running.  I'm not sure where that is on
an 87 though (or if it has one).

But I agree with Stuart; it takes a long time to properly bleed a
Vanagon.  I can now bleed the radiator without taking the grill off.
And do be careful over tightening those brass bolts on the radiator; I
had one break on me after I had just gotten all the air out.

Tom