Two things I found on my setup over the years. First make sure the pipe does not move forward and backward (a bit of rotation is OK but not too soft of a pipe mount). The forward and backward wear the o ring much faster. Second check your mount. The new Hyde mounts are much more efficient than older versions. I changed to one with a rotation limiter and have been running the same O ring since last August. Probably about 25 gallons through the setup and no leaking around the header. The engine compartment and pipe tunnel are clean.

Good luck,
Don