Grab something like a CYMA 15 tooth or Rocket 14 tooth to replace. You might want to correct AOE with some spacers, it's not 100% necessary but it's something I would do personally. I'd also epoxy down the rack, again that's just me. Thread-lock that gear screw and the piston head screw just to be on the safe side.
The height of pistons actually vary slightly, generally around 0.5mm. From the looks of your piston, it's similar to the E&C design which is one of the larger bodies. It's about 0.6mm taller than the XT / Rocket pistons I've got