Isn't this the same CM6 plug that is used on the 3W and DA motors? Doesn't it use a copper gasket on the plug? The only thing that I can think of that would cause it to come loose is if the head is overheating. The aluminum will expand a lot more than the steel spark plug and it'll get loose. I have never had a plug come loose on a 3W. I would talk to RCS and find out what they think is going on.