Those diffs were meant to be sealed.
Very nice looking, I love it, but the plastic Associated diffs are going to drive you nuts if you run it more than once.
With 2S1P 30C lipo I'm getting around 35-38mph out of the 5700, and around 42-44mph out of the 6900. I'm geared 25/72 with HPI X Patterns.
I had to completely tear my TC3 apart after the first body... 20-25 packs worth, to rebuild almost everything. The plastic just doesn't hold up. I can't imagine it holding up while being completely exposed. The top of the stock diff cases have holes in them, and mine sucked in enough dirt to a diff ring or two... or four.
I also had a blowout without the
belted X-patterns with my NiMh's.
You should also look into the NTC3 steering. The swing-rack is another headache in itself. I think, with that chassis, you can use the NTC3 stuff without modification.
I still love that chassis, I just wish they would have sealed the diffs.