Hello Freddy,

I haven't had that problem but one of my buddies did, I use the VITON O ring form Central Hobbies, VITON is far better than the Nitrile one from Hattori, and we found on my friend's that the header flange at the engine side distorted with time causing the problem, the latest Hattori header fixed this as the flanges are stiffer.

Hope this helps

Best regards

Alejandro