You need to loosen the clamp that holds the header to the rear section. You might be able to do it without removing the rear plastic cover.
After everything is loose, wiggle the header pipe until its clear of the cylinder studs.
Then its just a matter of twisting the right way to get it out.
There is no real reason to damage the graphite seal. When re-installing make sure to put everything in place before tightening any nuts or clamp.
Make sure the the rear clamp is tight and there is no exhaust gas leak.
04 KTM ADV 950S GO!!!!!
09 KTM 690 ENDURO R