If those skids are like the ZR chassis or the new F chassis, the bearing inner rease tends to seize to the shaft that the idler wheel secures to, there is a C-clip that secures the idler wheel bearing into the idler wheel, this c-clip is mounted inboard on the idler wheel and almost impossible to get out with the skid in the sled. I usually remove the skid, remove the c-clip, used a puller (or can use a piece of wood and hammer) and force the idler wheel off the bearing, the bearing will remain on the shaft, you can either use a puller to get the bearing off the shaft or I have cut the bearing off with a dremel tool, put new bearing in the idler wheel and put c-clip back in, lightly sand the rust/crud off the shaft, put some "never seize" on the shaft and slide the idler wheel/bearing combo back on. Good luck.