Take a look at this:

http://www.gowesty.com/starter_story.htm
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what a bunch of snake oil in my opinion.  in 15 years of driving and
working on vws i have never had a starter fail.  on top of that i have
never owned a car with less than 100,000 on the clock.  proper vehicle
service and trouble shooting is what this problem that gowesty is
rattling on about is fixed by.  but gowesty can't work on the whole
countries vanagons since they are in cali so why not sell a magical fix
via the interenet.  the real problem like so many problems on older
vehicles is a failing ground system.

lucas says the following:

Replacing the starter with a rebuilt Bosch unit would remedy the problem
for a while, but sure enough within a year or two max, the SAME EXACT
problem would return. For years I thought about this problem and wondered
why.

thats because he disturbed the ground system enough for the starter to get
a half assed ground for a couple of more years.  then when the oxidation
built up again that stopped the starter from working properly.  the real
solution is not a bunch of relays and fancy pants starters.  its to
inspect the aged factory wiring and bring that back up to snuff.  then your
starter will work fine.  on real rusty stuff here in the midwest the super
cure is to run dedicated grounds to things and not rely on chassis grounds
going through a rusty high resistance body.

jonathan