Hey guys I'm just posting this up so MP7 users are aware of a potential defect with the stock TM MP7 cylinder head. In the last month I've worked on two TM MP7s (both stock), one had a jammed mechbox while the other operated with no issues.
Anyway on both occasions after I disassembled the gun I noticed chunks of rubber broken off the cylinder head damper pad (dunno if that's what it's called). Again on both occasions the rubber bits were then pushed up elsewhere against the rubber pad which caused an uneven striking surface.
This caused one of the MP7s to break its piston head (about 1/4 of the plastic head broke apart into pieces) while with the second MP7's piston head developed a large crack on the surface. Unfortunately I don't have pictures of this part because I'm an idiot and threw out the piston head without thinking.
Attached is a picture of the cylinder head and the rubber pieces, the damage on both MP7s was in the same location. I'd love to hear what other MP7 users have experienced when working on the mechbox.
I hope this helps those of you who have experienced failures with the TM MP7.