Hello Paul!

My suggestion to you on this topic would be, "It depends."  It seems like that is always the answer to a sailing question, but let me expand a bit.

The Amel metal muffler does have a finite life, although ours is still going strong at 25 years, and pushing 9000 engine hours.  I have never heard of one failing catastrophically, but rather they seem to develop slow leaks that grow slowly, giving you the luxury of selecting the time for replacement.  If you were heading off to the remote islands in the South Pacific, this might be a good time for a little proactive replacement since getting an alternative would be expensive and difficult.  On the other hand, if you are coastal cruising in Europe, I would suggest waiting, since a replacement is relatively inexpensive and fast and easy to source.

Bill Kinney
SM#160
Harmonie
Annapolis, MD, USA
http://fetchinketch.net