This rubber is EPDM, not Nitrile (Buna-N). It is not very resistant to
petroleum oil, especially light solvent oils. Even petrolatum (Vaseline)
may damage it over a period of time. Certainly penetrating oils and
solvents should be expected to damage, even melt, it.
Use vegetable oils instead, olive oil, castor oil, etc., or teflon
powder.
I used to have a bottle of "One Puff's Enough," a sort of silvery
pearlescent whitish powder that worked really well on rubber and plastic.
Al