Don't get the piston with the metal teeth, the stress comes down to being on the teeth or the gears. Just use the stock CA reinforced plastic cylinder. I shredded one of those cylinders with metal teeth in about 2 months

Costs 25$ to replace the cheap piston instead of 100$ for the gears. Also if you're using just a 120 spring, I don't think you need the reinforced gearbox if you're short on $$.