Garlock sells, what, a thousand types of gasket material?
... and their products go into, what, a million other products?
I admit it; I have doubled up on gaskets or o-rings, in middle of the night type situations, with modest success.
... but in general, it's not a real good idea. For one thing, the doubled thickness may mess up an assembly stackup so that you stop the leak, but some other part doesn't work right.
Mike Halloran
Pembroke Pines, FL, USA