Loctite 5920 - Exhaust manifold sealant?

[Jay-ZS+]

Got a bit of an exhaust leak on the bike where the rear headers meet the block. They are only secured by a spring and although there is a copper gasket it doesnt pull tight enough to fully seal it.

Ive used a RTV silicone on the rest of the exhaust joints but not sure it would withstand the temperatures next to the block.

Found some Loctite 5920 that apparently can withstand temps of 350'C, anyone ever tried it or a similar Copper based RTV sealant?