Does 2001 XJ factory style muffler use a gasket (to CAT)?
 

Is there a gasket or not
https://cimg1.ibsrv.net/gimg/www.che...c5d8234ec4.png
on the front of the muffler where there appear to be two or three studs/bolts that attach to the rear end of the CAT? Thank you.

No.