<<My sense is that there are a few problematic areas related to the
cooling systems on these>>

The only problem with the water cooled Vanagon's is a no PM issue.

No maintenance spell's troubles.

How long should a hose last?
( I think they should be changed at least once every 100,000 miles
whether they need it or not )

How long should a cooling system go without servicing it?

A simple flush bi-annually would prevent and eliminate most of the
wasserboxer's problems .

But not too many folks are into the dirty work, or are much too frugal (
I held back with cheap ) to have it done.

Hence the wasserleaker.

You can't blame the Van.
Blame the people that owned it.

If you change all the hoses, and flush out the cooling system, It should
be good to go for some time, and many miles.

Sounds like you aren't to certain what to do here and need a push prior
to jumping over the fence.