Tam4511
CI BOOST FIEND
it would push crank case pressure and maybe a little oil out, that would not directly effect performance at all. I.E it wouldn't cause any sort of loss of power.Highly doubt it would be running at full potential if he could feel air coming out from the gasket.. That is asking to lose all your oil.... but don't se why it would cause the mass loss of power he says he is getting.
If you are losing power then id get a compression and leak down test and go form there.