I was about to say leave it alone and switch to the OD097T until I read about the plug damage. Slop in the crank, rod, pin, or piston pin-holes could definitely cause this as has been mentioned. As a rule, I will only use OD097T plugs in my 2 GXII's. Regardless of temps or humidity they run perfectly, but mine are both unmodified so Murnan may be where you have to inquire for your plug choice. If he says the OD097T should still work, definitely give it a shot. The P3's never last long at all for me.

Not sure about the refueling thing if there's a question about the tank, but you might try the this plug and give us a shout back on any effect.