Got the leak fixed. I took the old gasket off and put on a better quality one. From the inside of the car while driving, it sounds like a mustang with some quieter flowmasters on it. I have a stock catback on.
I've got a P0053 code now, I suspect it's a bad wiring job on the rear o2 sensor. I couldn't get the factory one out of the old downpipe, so I bought a universal Bosc and had to splice the wires together. I'll take it back out soon and see if one of them came loose. They are held together by some funky twist-lock connectors that came with the o2 sensor. I think I'll switch over to a more conventional crimp instead.
