Burned out Motors

In our last competition, one of our motors started to fail to respond, upon taking the motor off, our driver noted that the motor had an odd rattle to it, we were able to snag a replacement from another team. Once the competition was over, I decided to check out the rattling and once I opened up the back of the motor, the bottom of the two midsize gear came out, I shook the motor a tad bit to see if the other would fall out and it still seemed to be snug. I was curious if there is any way to fix this issue, as although we can buy new motors, it would be nice to be able to fix them and keep using them if this is the only problem. Thanks for the replies!

motor refirb kit is available: http://www.robotmesh.com/vex-motor-393-refurb-kit

It has a replacement for all the motor gears.