> I think, the chemical engineer, who designed the mix for the plastic, has
> made it for early disintegration, as planned obsolescense.

Nah, it's not so much "on purpose" as it is "cheap". I once had a plastic
and rubber guy explain the chemistry of it to me. I don't recall the
specifics because I don't know one long chain polymer from another, but the
practical upshot was that black plastic uses a more UV/ozone resistant
(plastic chemistry stuff) which happens to be black in color. In non-black
pieces, a different (plastic chemistry stuff) which is  white/clear has to
be used to make it colorable, and that stuff is a lot less UV/ozone
resistant. Additional chemicals can be added to make non-black pieces more
durable, but it's usually too costly for things designed to be relatively
cheap to make (like car trim parts).

--
John Bange
'90 Vanagon - "Geldsauger"