I have an '82 240 and am doing maintenance during the pause in our riding season. I've had several people tell me that it's important to cut the pipe open and replace the internal packing. I don't have a problem doing the work but I can't get anyone to tell why it needs to be done. I understand why I need to repack the muffler but the pipe makes no sense. I can push a piece of tubing clear through. Anyone have an explanation? 

They get very heavy due to the oil soaking the sound absorbing material and the buildup of carbon deposits. I've reduced the weight of a main chamber by over 1kg by cleaning it out.

The sound absorbing material in the main chamber stops absorbing sound when it gets oily and when the mesh holes get blocked.

On some exhausts the performance of the motor relies on the harmonics inside the main chamber and this can be affected by the holes in the mesh getting blocked.

There will be deposits inside the header which might not stop you pushing a tube through but it means that it is no longer the ideal diameter and surface drag for ideal engine performance.

Thank you very much for that detailed explanation. Time to open it up!