+1 sounds like your motor height was not set correctly. Make sure it is set properly now or you'll just wreck another gear. No need to get a new set of gears IMO if yours are still in good shape KA makes decent gears.
Make sure you're cronying with the same weight bb every time. If your FPS is inconsistent check your compression, a metal shard from your stripped gear could have wrecked an o ring. An M110 spring should put you at give or take 380 fps, M100 360ish FPS. It's possible the guy who changed your spring in the first place got a bad crony. You'd need a weak spring or a heavy bb to get 300 FPS unless your compression is bad.