mate, your gear box stuffed, could it due to lack of mainatance, or lack of quality selection, or too much tension on gears...

I use tamiya gear box plus home made 3 in 1 reduction. I play hardcore like anyone else. But I have to admit I did a slight mods on the bushings to the gear box. So it has been 4 years so far, I play on sand as no one else would do.... Its tough.....

here is some of my videos......

http://www.youtube.com/watch?v=Ynib-LY7TSY

http://www.youtube.com/watch?v=8yFeC6OXIi0