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.
Well over 20 yrs I'v had my Keihan's on the outfit and they're superb. But they have both cracked in the pillion support area. I never thought that the omission of that little tab would be the cause. Of course both my tab's have broken off.
Other than welding, is there a Meccano fix for this?