My flex pipe rotted out last winter. In a bind, I went to Meineke where they did a patch job welding in a new flex. I am wondering how much the exhaust flow is disturbed by the new piece's slightly smaller diameter creating a little lip in there. I want a whole new flex pipe now, connecting from the header's downpipe to the cat. My cat is original so do you think it is too rusty to connect to? Where can I get a new flex?? How come no one talks about high performance flexes?