How to fix an airsoft gun (power)?

I have an mp5 blow-back aeg and I tinkered with it. My motor was going off automatically and I took of the motor, but left the motor in the pistol grip. I was still putting it back on and pushing on it while my friend accidently put in the battery making the motor run and probably wearing some gear down. I fix my automatically shooting airsoft gun with wiring, but now it shoot 2/3 the distance it shot before. Do I need to replace some gears, get a performance upgrade from a good airsoft retailer, let the pros fix it, send it back to the company and pay their fees or something else entirely. I am thinking of going to a well known airsoft store like Airsoftgi and let the pros fix it.