Put some Ofna steel gears in the UE.
http://www2.towerhobbies.com/cgi-bin...?&I=LXCWK1&P=7
These gears drop right in to the UE spyders and are steel. They work great and give you a bulletproof diff. If you want a hardened steel version, get these:
http://www2.towerhobbies.com/cgi-bin...?&I=LXCWX7&P=7