When your header pipe and your muffler are very attached to each other and don’t want to separate no amount of external pressure can break them up without destroying the relationship.
It is odd; not 2 weeks ago I took off my header and did not have any problem. Last night when I was pulling these apart again, the muffler gasket stuck to the header and refused to budge. The back half of it was stuck in the exhaust pipe. Since the gasket material is soft and friable the only way to seperate the pipes was to destroy the gasket.
The good news is that I got to see how the gasket is made (brillo pad covered in binder/insulating material) the bad news is that it required a trip to the Yamaha dealer and $15 for a new gasket.
My only suggestion to others would be to attempt to rotate the pipes before pulling on them. I believe that there is less chance of destroying the gasket if you can break it loose rotationally.
See if you can guess which is the old and which is the new:
Part number 3YF-14714-00-00