On plastic rot.

The plastic creators keep improving their product. Cars from the 60s
where the first to start using large amounts of plastic, and it has
gotten so that more and more plastic is incorporated into subsequent
model years. Early plastic was not designed (and couldn't tolerate) UV
and high temperatures. As real world experience as progressed, the
plastics have gotten better. The Vanagon's date from the 80's (mostly).
So the plastic lasting 20 years (or so), is quite reasonable (from a
manufacturers position). Life expectancy of a car being 10 years more
or less.

This reminds me of a tale I heard regarding Russian planes in World War
II. The russians did an analysis which indicated that their planes only
last a couple of weeks in combat. So they designed them to only last
about twice that long, figuring they'd get shot down before they fell
apart. Probably a myth, but the point is, Most makers have to make a
lot of trade-offs in manufacture. Some of the trade-offs are durability
versus expense. If something is "good enough" for the expected life
expectancy, then they'll likely use that, rather than some more
expensive item that will last forever. Brass over stainless steel.
Rivets, versus screws. Plastic versus metal or wood.

You each make that same choice on every repair, most likely. Junkyard
part versus new from dealer. Why blame the maker? I'm just thrilled
that my Vanagon works as well as it does, 20 years after it was made,
and that parts (mostly) are still available, and alternatives (engines)
are available.