Wouldn't be cheap, I have a full set of tread files and if my exhaust tread needs cleaning up I just run the tread file around it, have only needed to do this once in the 36 years of owning my 850 I always make sure when screwing the exhaust clamps in that they start smoothly and sit straight before tighting them in, plus I make sure my headers sit loosely in the head before I do the clamps up.
Ashley