Briefly, there's a rattle from the engine compartment whenever I'm
accelerating, and I wonder if I should worry about it; and I'm
wondering where I can get an oil temperature sensor in the
northeastern US (in Illinois, Indiana, Kentucky, Ohio, West Virginia,
Virginia, Delaware, New Jersey, Pennsylvania, New York, or the New
England states.)

More detail follows:

Cram-It in Omaha charged us 7 hours to take the engine out, 14 hours
to put it back in, and sent it out to John (who repairs VW engines) to
look it over.  We had burned through one of our pistons, and another
was very thin.  John replaced the scored cylinder and those two
pistons and pronounced our crankshaft OK.  (Are these labor charges
reasonable?  I thought it should be more like half an hour to take it
out and an hour to put it back in.  They didn't bother to replace the
rest of the ancient fuel injection hoses, which are probably about to
go, but they did put on a new V-belt.)

(I've replaced five of the high-pressure fuel injection hoses myself
with 7.9mm ATF cooling line, but that was because I had three separate
leaks.  I'll replace the other four or five ASAP --- I just need to
get the clamps.)

Since then, there's been a horrendous rattle whenever we're
accelerating.  Cram-It assured us it wasn't coming from inside the
engine.  They left a loose 10mm combination wrench in the engine
compartment, which presumably caused some of the rattle, but even
after I found the wrench and removed it, the rattle continues (less
loudly).  Should I worry about this?

They filled the engine with 20W-50 oil.  Is that OK?  I heard a rumor
that multiweight oil generally didn't work very well in these
air-cooled engines.  I don't know what brand they used.

Now the starter doesn't start the engine when it's hot.  It turns
over, but only slowly.  If we let the van cool off for a while, it
starts OK.  Cram-It tells me this is a result of the starter being
old, although it was replaced by a previous owner in 2003, and that
taking things apart and putting them back together often reveals
latent problems like this.  Should I expect the problem to go away if
I put a new starter on it?  Are junkyard starters a good bet?

Presumably we destroyed the piston by driving the engine too hot.
Several people have recommended adding an oil temperature sensor to
avoid this.  I understand there are a couple of kinds --- one that
replaces the original oil drain plug, and one that replaces the
original oil pressure sender with one that includes a temperature
sensor.  Which one is better?  Is there a place we could pick one up
on our road trip?  Since we're traveling around, it's hard to
mail-order things.  Our current itinerary takes us through Illinois,
Indiana, probably Kentucky, West Virginia, and Virginia, to D.C.,
Philadelphia, and Boston, where we have family and friends; but we
could reschedule a bit.

Sorry for the lack of posts --- my laptop screen hinge broke, and I
haven't gotten around to replacing it yet.  I can't use the laptop
when we're on the road this way.  Replacing it involves, basically,
taking the laptop completely apart and reassembling it.