I hope someone can help here. After the up pipe where the y piece fits on, i cannot stop it from blowing. I have taken it apart and cleaned both faces, then re assembled with a new clamp. Still no joy. Should I have to use some sort of sealant? If so which one please? Any help appreciated, thanks gents.

You need a new gasket ....

Is the graphite seal/ring ok? Is there one?

I have replaced the graphite gasket off of the rear header pipe. Im talking about where it joins to the y piece further up, where the pipe is widest. Should there be a gasket here too? There never has been since i had the bike!

Wrong joint, guys.......................the joint at the y-piece does not have a gasket and has always leaked, albeit only a little, on mine.

Ah yeah, I see where you're talking about (had to look at a pic to figure out )

Have you tried loosening the cans to see if you can get it better aligned.

Yup tried that too!

Do you run the original exhaust mate or do you have a set of cans fitted?
Some aftermarket cans have some "loose" tolerances I had to "work" a bit on the hangers for the Mivv's I'm running to make all fit snug and align the joint.
If the clamp is worn out it doesn't fit tightly and you need to replace it, the V shape widens. (edit, sorry you done that)
If you run original exhaust and you made other mods like SAS valves and maps the cat might be clogged, the pressure needs to go somewhere and it will leak anywhere it can.

It's akra cans and y piece. Standard headers, no cat.