The deal is any metal that is in constant contact with saltwater needs to be connected to the bonding system.
If you have attachments, as you say, on your non metal muffler, they will not need connecting to the bonding system as they are not in contact with saltwater.
You should be able to decide what needs bonding and what doesn't based on the first line above.
You can check if things are bonded or not with a multimeter, one probe on the main bonding connection, or something that you know is bonded, and the other probe on the item in question.
If it's bonded you'll read continuity on the ohms range, ie very low resistance...if it's not bonded the reading will be open circuit or maybe many megohms.