I had a friend brother try to install a off road x pipe to his stock catback and they said it didnt work to good...it fit, but for some reason it leaked alot because of the pipe size going from 2.5" to 2.25"....reason I ask is my car has the stock 2.25" piping, but the previous owner welded in flows not that long ago, so I kinda wanna make sure of the stock/flow catback instead of spending $400 for a new one...will I be ok?