I hesitated posting this, but best to be informed, check your MIJ exhaust with a magnet, if it sticks I doubt it is 'proper' T304 steel.
I need a whole new exhaust soon and based on my research I would go to Primary Designs as a first choice. Pricey I know, but it is for a S8.
http://www.primarydesigns.co.uk/
I have visited them before, they are very friendly. People who can make Inconel and titanium exhausts must be quite skillful.
As a second choice and on a budget I would go to Infinity-Exhaust in Bristol. Lots of good reviews on the web and on pistonheads for what its worth.
http://www.infinity-exhausts.co.uk/
I am just a web digger, best to trust your own research
