The micro adjust clamp of my seatpost often slips my 200+ pounds hit a hard bump (little ridge things are worn down). I was going to replace the seeatpost but noticed that neither Nashbar or Performance carried the right size. The seatpost is stamped 31.4. It's from a 1996 Mongoose NX73 mountain bike. Are 31.4's still out there? Or, will a 30.9 or 31.6 work without needing shims?