AirMaks Arms Airmak krait plenum leak

Hi guys my m8 bought a second hand krait. Couple of weeks later an his plenum seals started leaking. He tryed changing all 4 with new oringal seal but they just seem to big really tight an keep breaking on the threads as it get screwed in. Is this normal or is it more than meets the eye
 
Verified leaking at both ends of the plenum how or what method did U use to identify the leaks? O-Ring 17x2 90NBR ? Did you apply some silicone lube?
Definitely the plenum. Yes loads of silicone lube it's like they to big an just cut up wen screwing in. It's even hard just to push in before you even start tightening up. He bought a seal kit maybe just order them seals on it own from somewhere else