This is the exact reason I will NEVER use the Hooker mufflers again, same thing happened to mine, rotten things rusted to hell inside the tubes. What I did was to spray a whole can of WD40 into the tube from each end, PB Blaster or other solvent can be used with better results I would bet. The WD40 didn't work very well, so I had some used oil waiting to be disposed of, I poured some of that into the tubes, made a huge mess.
Take a 3 inch piece of wood/metal tube and wrap a wire or strong cord around it securely. Then take the cord and fish it through the muffler from the exhaust end of the tube. Have someone hold the tube or secure it some way then yank on the cord all day.....that's what I ended up doing.
Once you get them out and the STS baffles installed you'll never have this problem again. If I didn't like the looks of sidepipes so much and spend so much money on them I would have smashed them into tiny little chunks of metal, that's how ****ed I was at those mufflers.