Here's the scenario:

81 Vanagon 2.0 auto.  Came into my life running on three. Nothing in
the way of compression on #1.  Good friend had a motor with 43k
original on it.  Swapped motors.  New old motor has 120 +/- on all
four.  Old old motor sits in shop awaiting teardown.

Drive Vanagon ~2k miles.  Starts easily, runs strong. Uses about a pint
of 20W50 every 500 miles or so.  No visible leaks, so I assume the it's
burning it. Sell Vanagon to a good friend. (Who has owned and driven
many VWs though never a type IV motor. Type I sorta guy.)

Tear down old old motor. (A SIR rebuild with 12k on it.) Find a divot
out of the #1 piston at the top of the bore.  About 1.5 inches from
start to end. Looks like maybe it stuck a ring.  Divot extends down the
side of the piston to the oil control ring. Cylinder head has damage
equal to what one would expect from compression ring pieces floating
around. (pictures available) Figure a cylinder and a piston will fix it
good enough to go in the bay window for a year or so.

A month goes by...

Friend calls from the side of the road.  Go rescue.  Nurse it 70 miles
home. Pour 2 gallons of oil through it getting it the 70 miles.  Friend
pulls new old motor and pops the head off.  Guess what?  Exactly the
same damage on the same hole. Why?

The new old motor had nothing of the old old motor.  Different FI,
different ECU, different everything. (It was a complete engine.) It was
not low on oil. It had the correct Bosch plugs and was timed to
specification. It was a hot day and the failure occurred at the end of
a long pull. Probably under about the same circumstances as the first
failure. The other three holes show no sign of detonation or
overheating.

At this point I'm at a loss.  What would/could cause two identical
failures on completely different engines? What can we do to prevent
future failures.

Jim