Wazzer: you don't need a gasket on that joint mate. just some high temp red silicon does the job perfectly. it's what everyone with a relentless downpipe uses and no reports of failures yet. mine's been on and off several times and sealed up perfectly with the silicon each time.
Also, if they have supplied a turbo - downpipe gasket, DON'T USE IT!!!!!
Only ever use OEM gaskets on the exhaust sytems, the perforated style ones won't last long at all.
Also, with regards to the mikalor clamps, by all means use them where space is very tight, but you'll probably find they don't offer much resistance to the two sections rotating against each other. they're a fantastic clamp with a very circular clamping force, but if the exhaust has the chance to sag and twist away from level, it'll most likely do it with a mikalor clamp on there.
One combat option it to get everything lined up and clamped, then put a tiny tac weld in just one place on each joint to stop rotation. easily chipped off with a chisel to remove, but keeps it all sitting nice and square to stop it banging and knocking.
Mines at the depot ready for me to collect now
