What types of Oils Don't damage Rubber

[Einhorn Hofmann]

I wanted to learn more about which types of oil will (and won't) generally
damage rubber.  I was curious, for example, about synthetic ATF's, such as
Mobil 1 ATF?

Its accepted that if you get conventional motor oil on conventional rubber,
long term its going to cause damage.  For example a car with a leaky rocker
cover gasket spraying off a bit of oil, and after a while many of the
vacuum hoses are swollen and brittle.

In contrast, Pentosin oils in the hydraulic system actually run through
rubber hoses.  Is this because the rubber is specially resistant to oil, or
because the Pentosin oils don't damage rubber?  I'd have assumed it was as
simple as "Synthetic" are rubber safe, but before there was CHF 11S, there
was CHF 7S which wasn't synthetic, yet specified for the same vehicles as
11S for a few years and running through the same rubber hoses.

Mobil 1 engine oil is marketed as "fully synthetic", yet further reading
and I find a comment, "Mobil 1 is not a pure synthetic. It has a fossil
base.".

Similarly Mobil 1 synthetic gear lube, that you'd use in the final
drive...wondering if it damages rubber.

Thanks for any thoughts,

MC