What oil for compressor non return valve?

[tight fart]

The non return valve is sticking in my Sip compressor, I'd discribe it as a rubber bung held in position by a fairly light type spring. I gave it a squirt with a silicone grease and it was ok for a bit but not that long.
Is there a correct oil to use?

[E-bmw]

If it is on an air compressor I suspect it should be dry, as otherwise all passing debris will stick to it.

Just replace it, the type that you describe are generally non-serviceable.