An update for those that may have a similar issue some day....
I fixed the leak. The manifold side of the connection has a stud screwed into it. The cat pipe flange slides over the studs and is held on by nuts. The studs are not threaded the full length plus they have a shoulder about half way up. That combination was preventing the cat pipe flange from moving closer towards the manifold and tightening the joint. Tightening the nuts on the studs more just clamped the flange tighter against the studs shoulder.
The solution was to use a dremel tool to grind off the shoulder and slightly drill out the bolt holes in the cat pipe flange so the flange can freely move up the studs closer to the manifold. Reassembled and torqued to 30 ft-lbs and no more leak.
Last edited by s27payne; 09-21-2013 at 10:05 AM.