Thanks to all of you who passed on your hints.  As luck would have it,
spraying the nuts/bolts with penetrating oil did the trick.  The fact that
it's always been a southern California vanagon helped with the rust too.  I
did need to loosen the muffler brackets and shift it a bit to make the fit
but that went pretty easily too.  I decided to replace the O2 sensor just
because.........and then I changed the oil and filter.  Then the kids (11
and 13) washed B.O.B. (Bucket of bolts) because, as they say, the Vanagon
"rocks", and it's running and looking great.  I knew that this was a rather
easy fix (if the bolts came out) but it helps so much to know that I can run
to the computer and get help.....just in case.  And I still had time to see
family and stuff my face on Memorial Day!
Debra