Just check on ebay for e-maxx tranny's and buy the Hardened steel idler from rc-monster. Get some CVD also if you can and don't forget to do the fuel tubing mod for the center drive cups.
The tranny is easy. Mike sells all those parts needed. basically just need the top shaft, second gear, and a steel idler, that's it! Real simple. Oh, and the bearings for it....
"if you've got something to say, say it peacefully"