after reading all your stories i was worried as id just bought a magnex cat-back exhaust 6" oval for my 172 mk2, so when i took my exhaust to have it put on i told the guy putting it on the problem & he used the renault mount the extra magnex mount and he fabricated another 1 its brilliant, able to move slightly but no noise at all & very strong!!! i live in bham & the guys called dusty ,he works for wheelworks in balsal heath. i recomend anyone with this problem who lives in the west midlands area to go and see him!
ps. it sounds and feels brilliant, like having a new car !!!