- A common fault on E46 M3 models is failure of the exhaust flanges caused by rust / corrosion of this part. Four flanges are used to clamp together and seal the intermediate pipe to the rear muffler / backbox. These are constructed of cast iron (despite being fitted to a stainless steel exhaust) and inevitably deteriorate and split. These parts are integral to the intermediate pipe and rear muffler and are not available separately from BMW. The only option until now has been to buy a new centre section from BMW at vast expense. Or to buy new flanges, cut them up, fit and re-weld them- a tricky job. None of these are an ideal solution to this common fault.