There are (obviously) some types of rubber which are fine with petroleum
products, but most are not. The worst petroleum offenders are the most
volatile
ones, like gasoline. Vaseline is a rather heavy, non-volatile, compound
which
whose effects should be minimal.
On type 3s, it is clear that the rubber oil filler bellows is quite happy
with
oil, but if you take a look at the rubber "gasket" under the "base" (where
the
dipstick screws in) is a perfect example of a rubber that is NOT
compatable
with oil. Those should have been made from a different material, but they
weren't.
The bad effects consist of the petroleum compound soaking into the rubber
and
causing it to swell and soften. I suppose that a limited amount of this,
like
you might get with vaseline, might even give good results. But most of the
time
there is also a long term degradation of the rubber compound.
My resource for this is the Parker O-Ring Handbook. It is an extremely
useful
compendium of information on the properties of various rubber compounds
and
their compatabilities with lots of various fluids, as well as a listing of
all
standard US sized O-rings and design specs for designing proper O-ring
grooves.
Don't ever pass up the opportunity to grab one of these.
--
Jim Adney