I recently picked up a TX311 frame, exhaust, rear suspension etc. I just bought a TXR312 last night in need of a lot of work. What are the differences between the two models (besides rear brake and shock)? The frames look similar except for extra tabs on the 312 for shock, extra mount on mid muffler. On my 312 the shock is leaking oil, bearings are bad. Has wrong muffler. The 311 swingarm, shock, suspension bearings, frame, exhaust are all good. Thanks