Worth trying the Keihans 10yr Gtee? But you are a long way away. Also check that the little cross bracket on your pillion/exhaust mount is not cracked, they often are and can cause exhaust cracking.
I agree with Max on the Keihans, they seem to last forever and the ones I have fitted have all be sized properly.
The sports mufflers were built because of the Internet, Jim had been talking for a couple of years about getting some sports silencers made to his own design, I was on the Motobins forum at the time and put the word out so between forum members and Jim's own customers, we got the minimum number of orders together so that he could get them made. They look stock apart from the outlet that is of a larger diameter.