I bought one of cmmg's gas piston kits about 2 years ago for an ar15 build and last week the piston plug started leaking gas. I went on their website trying to find the part but they dont make it anymore. So i called them up to see if the plug from the new kit would fit my kit. Thwy told me "no, but if you send us your old kit, we will replace it for FREE!" thats a $400 gas piston system with a bcg for free.
So I mailed in the old on last wednesday and just got the new kit today.
Seriously amazing customer service.