I broke my silencer and don't want to do it again

Took the silencers off to change a tyre and discovered that where the lhs silencer clamps on to the pipe all the 'tines' (if that's the right word) were cracked. so I took off the clamp that I had loosened and wiggled all the tines and they all came off (must have been just held in place by rust ). I can't see how I have cracked these as the spacer/bush is properly in place. After thinking about it for a few minutes I realised that to all intents and purposes this silencer is now a dead duck. I have found a second hand one on ebay but am worried that I may make the same mistake again - what am I doing wrong ?
Mike