Due to some unfortunate circumstances I recently had to have replaced my rear driver's side caliper and it ended up coming loose while I was driving and the piston was forced out of the seal. Someone I know had a look at it and removed the piston and gear bolt and wanted to put it back inside the 'dust seal'? but found a tiny snap ring or something that came out when the gears were unscrewed. I was wondering if anyone knows exactly how it fits back inside and if the caliper can just be reassembled.

Originally removed from car.

Gears and piston with seal and snap ring?

Main caliper assembly.