I know, it's weird. I havent touched the gearbox in my G&P M63 and it's holding up fine, pushing 50k rounds through it now. Even the G&P gears are holding up.
I have not done a long term test on any CA pistons... but I just did an AoE adjustment on my AUG and left the stock CA piston in there, I plan on running it till it breaks to see how long it actually lasts.
I change primaries like other people change socks.