>> (1) oil weight  too thin- should be 20/50 not 10/40

My experience is very limited, having only owned my 1982 Air-Cooled
Westy since September of this year, but the only two things I did to
resolve my oil pressure warning light issues was to remove the FRAM
oil filter and replace it with the correct OEM Mann filter and change
the oil to a high quality 20W50.  I would at least start with that -
the two cheapest and easiest things to change - make them right and
eliminate them from the equation.  If the issue still isn't resolved,
I would then check for faulty wiring at the oil pressure sender, next
would be installing a new oil pressure sender.

 From there I can't help.  But I am a big fan of trying the simple,
cheap things first and eliminating them from the picture.

Everyone recommends installing OP Gauge, OP Temp and CH Temp gauges.
That's fine if you have the cash and the down time I guess.

Joe
1982 Westfalia/Vanagon L
Stratford, ON