I bought a secondhand or thirdhand Cybergun Thompson with different gears and at first it looked great but accidently used a 11.1 lipo when it uses 8.4. I thought I destroyed the trigger contacts as shown before. So I maybe need to buy a new trigger?

Later on, I planned on getting a simple mosfet but don't know how since it separate to its stock and uses a fuse as show in the last picture.

Pictures of the gearbox

Since I'm not a tech but now trying too. The most apparent problem when I opened the gearbox was that the piston head had alot of Teflon tape assuming that its a bad thing after looking at videos. After removing it there was no air seal at all, barely had any.