i use the filters that napa gives me and the first filter held for several months and the one before that never gave me a problem. all that aside i think i have come up with a possible cause for the filter leak. tell me what you think about this ---- when the motor is backfiring its shakin something terrible. maybe the shaking is hitting the filter against the frame mount or frame and bending it slightly, just enough to take pressure off of one side of the rubber allowing the pressurized oil to blow out past the seal. how bout that?!?!?

just a theory that just popped in my head. im going to inspect the filters for any warping right now. ill keep you posted.