Gun is fixed with regular crazy glue.
I did a full teardown as well and found the same sludgy grease that Colin described. Gobs of it everywhere. The piston head was misshapen. one side was a full 2mm off. Replaced it. Range and accuracy greatly improved.
Trigger return springs on these echo/jg guns all seem way too strong compared to marui/ca. It makes them a bitch to work with. Recommend changing them out.
Do all mp5ks have double-ported cylinders?
Grand Poobah of T.W.A.T.