Blowby in the engine is not gonna cause the oil leak where you say it is. So don't worry about that.
You have a real mystery... to me anyways. I just cannot imagine THAT rubber seal giving way. I can put that filter on there where it will hold 120lbs pressure! Is there any chance you are screwing the WRONG filter on it?
The bad running is something we can get to when your engine will hold it's oil inside..
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist