I'll toss in a couple of others:

13. AC connectors in D pillar for AC fans. Passenger Vans model years
86+, due to the way the AC housing is set up on Westy's this is less
likely to occur on them.

This can be caused by condensation drip, when the drip tubes are
misplaced, or clogged, water will come down the D pillar. This can
lead to corrosion of the copper wires (noticed as green at the
connectors) and increased resistance at the connectors (resulting heat
will cause browning of the otherwise translucent junction insulators.)
Emory cloth to clean contacts, you may need to splice in new wiring if
the copper is badly corroded. And of course, correction of drip tube
problem to prevent recurrence.

14. AC fan speed switch. 86+ Vanagons

Like other switches in Vanagons, VW seemed to like putting the whole
current through the switch, which can cause melting of the plastic,
and failure of the contacts. Replacement is the best course of action.