k12 1.2 Exhaust problem

Hi all, I just recently replaced the centre and back box on my exhaust and now it's blowing more than when the back box snapped off.
I went to euro parts for everything I needed and what they gave me was the middle and back section four rubber mounts and a metal ring for the Back box connection, is this really all i needed? I've put it together as it was before but copper greased the bolts and tightened it all up but is blowing.
Any suggestions as to what I've probably done wrong?
Thanks for any help guys.
 
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