NitroRCX is selling quite a few parts
for the BSD 1/10th, 1/8th, 1/6th cars which map to the Caldera/Shredder/Earthquake/Backdraft/Aftershock models: they also have the complete Shredder SC(aka "Mad Gear Tuscon") trucks on for a good price. You have to scroll down the page a bit, but you see things like complete diff units ($7.38!), bearings, diff housings and gears, outdrives, suspension pins/braces, shock towers, ball ends, steering racks etc.
It looks like those sale parts are part of them blowing out the Tuscon model line, but most of the drivetrain parts are also used by the 1/10th and 1/8th Redcat models I listed too. If you're not sure if the parts fit then don't buy them, but if you own any of those kits you can probably eyeball the parts and realize they're the same thing as the Redcat bits. For $20 you can get two diffs and a handful of bearings to keep you running a long time!