I pretty much did what Doom! said. I have an 8ight T RTR, I am new to the hobby and had a few head on collisions with cement curbs over the past several months. This caused the front shocks to pop apart at the top cap. After the 2nd time I decided to upgrade the shocks to TLR units. After checking what new parts would cost (they are not available pre assembled from Horizon or Amain) to put a set together, I checked eBay. I found a set of 4 for $100 which was 1/2 the price of new parts for just 2 fronts. They are working great. They are from the TLR 4.0 truggy. I wanted to make sure the lengths were correct and these were.
Prior to replacing the shocks, I went through all 3 diffs and upgraded them to TLR status. I also increased diff oil viscosity to what TLR recommended for the 4.0 truggy (7, 12.5k, 5 front, center and rear). I started the diff replacement due to trashing the center diff. Not totally sure but that was probably a result of one of my front end collisions too. Had to replace the front center dogbone too as it got bent somehow in the mayhem!
So far that's all the big stuff. I have also been changing spring rates on both ends. Currently waiting on even stiffer springs from Amain right now.
I love the truck and the hobby. Parts are readily available for Losi’s which makes it nice too. Hope you enjoy the truck.