Cheers mate, I think you're right the hardest bit will be getting the clamp off as it's spot welded on I think, what I might do is try and loosen it off pull the back box back a tad , smear sealer around the pipe and push the silencer back on ,so as to create a bead of sealer around the joint as it were,then tighten the clamp, knowing my luck though the clamp bolt will snap!!
Cheers Pete