Yes, it was me that reported that the oil pan held 4 quarts.  I cannot
explain the difference in our test results.  From Mark Drillock's
experience, I believe that I have the oil pan used on the factory TD Vanagon
sold only in Europe.  The turbo oil return line goes into the pan at the
bottom edge on the left side.  Incidentally, in the North American ETKA this
is the only diesel oil pan in the illustrations.  The oil pan commonly found
on the 1982-1983 USA model diesel Vanagons is listed by part number only.
All of the illustrations from 1980-1985 show the TD oil pan.

A few comments on the level of the oil return line:

I recently saw an illustration (like an engineering drawing) of the factory
1.6TD setup.  It shows the turbo hanging very low and the oil drain line
running very nearly horizontal to the oil pan.  The oil pressure in the
diesel engines approaches 100 PSI at higher RPMs.  Even with the predictable
losses after running through the filter and turbocharger bearing, there is
really no way that crankcase pressure could have a meaningful effect on oil
flow from the turbo to the oil pan.  Whatever crankcase pressure exists is
being vented anyway.  Some diesel owners here have voiced concerns about the
oil that remains in the drain line being thermally damaged through prolonged
contact with the turbocharger bearing after the engine is shut down.  This
is a concern with all turbocharged engines, and the universal precaution is
to allow the engine to idle for a few minutes until the oil flow has cooled
the turbo enough to prevent oil coking on the turbo bearings.  The oil does
not drain completely from the turbocharger bearing, regardless of the
location of the drain line.  Whatever oil remains in the bearing is
susceptible to coking.  Personally, I believe the thermal stability of
synthetic justifies their cost in turbocharged engines.  YMMV.

In the 1.9TD engines, VW moved the oil return line to the engine block.  It
is well above the oil level in the pan.  Would they have done this if
crankcase pressure could cause damage to the turbo?  The most compelling
reason is so they could discontinue the production of the various models of
oil pans for various turbocharged vehicles.  I have a 1.9D 1Y engine block
in the garage.  It has a raised boss cast into the side of the block in the
same location as the oil return hole on the AAZ engine.  It also has the
same piston squirter oil nozzles as the AAZ.  It appears that the only
difference in the engine block is that the factory did not drill and tap the
hole for the oil return line on the NA block.

Mike Snow