The original Yam silencer was made from good steel and only ever seems to suffer from surface rust. A good wire brush and spray with satin black gets them looking new. If the stainless decorative collar is damaged then it's simple to fit a replacement - only 4 rivets!
The only problem occurs with putting the TTR away with wet mud sitting on the exhaust's front pipe. Even good steel will succumb to rusting with this treatment after a while