I have seen where people have rebuilt Gas Gas mid mufflers so decided to give it a go on a Rev 3.  There is much less space in the rev 3 muffler between the perforated pipe and the outer housing.  The packing was wrapped around the perforated pipe and not in real bad shape so it was a major PITA to remove.  Much time was spent tearing and pulling with long needle nose pliers and a wire hook for installing springs.  There was a lot of carbon dust/ dirt mixed in with the steel wool.  It was replaced with course stainless steel wool from eBay.  It was pretty easy to push the new wool back behind the perforated tube.  Patches were made from 0.032" 2024 T0 aluminum and riveted on with high temp RTV for sealant.  The T0 material is very soft and sort of like thick aluminum foil used in the kitchen.  My sheet metal skills are not great so the patches are not pretty but cannot be seen when mounted on the bike.  The end result is a quieter bike with smoother off idle power.

 

 

 

It would have been nice to know something more than the price of cat litter!

Looks like a good job well done to me.