leaky y pipe from lpp

so i finally got around to putting on my new lpp longtubes and there awesome dont get me wrong but i just cant get the y pipe to seal up.i used band clamps like everyone on here said to do and put some copper permatex where the pipes overlapped but i can still hear the exhaust leak and when i crawl underneath i can physically feel air coming from the y pipe i checked and all the clamps are as tight as they can be. so here's my idea i wanna run by yall. ive got a pipe expander so i was thinking about enlarging the pipe so the fit would be nice and snug but part of me says that the band clamps just arent doin it. i really dont want to pay 50 bucks a clamp for those really good ones but the u clamps crimp the metal so if any one has any input on what to do please let me know. also is it common for the y pipe to rub on the front driveshaft?

None of the clamps give a good seal. I've been through every clamp(except the u-bolt) I know of to try and fix my leaky header collectors to no avail. I finally bought some ball and socket connectors and I'm going to weld them on sometime this week, hopefully. I'll let you know how it goes. As far as the driveshaft clearance, it is a tight fit and sometimes it needs a good whack with a BFH to not rub.

Try V-Bands.

I welded all of my joints and no leaks!!!

I just got done installing the ball and socket connectors on the header to y-pipe connections. Best thing ever. Nice and quiet and easy to assemble/disassemble.