I would just use google and see if you can find something for a How-To on the trackwheel. Honestly, you could maybe
fix it but you could also spend $50 on the part and then fry the device trying to fix it. My recommendation is to just replace the BB. There are some great devices out there. Upgrade to the 8320 and get wifi/uma, a camera, and media card support. If you're in contract and can't get a subsidized price then check the buy/sell/trade forum here for one. I've seen quite a few come through. I suppose it just depends on how adventurous you are.
If you really want to save the device we have a member here who has a repair shop. He is ShapelessBB on the forums here and has this store: HorizonWirelessOnline.com - Horizon Wireless, Canada’s Cellular Repair Center ß