I'm about to service my gearbox due to the gasket on the sump failing.

My question is do I use sealant on the new gasket and if yes what's best to use?

I always struggle to believe a dry hard paper gasket will seal so I always use a little selant,i use 'blue hoylemor' or 'haemetite'[am sure I have spelt both them wrong],just a faint smear to both sides making sure you get no lumps on the oil side,not had a problem !

Make sure the sump sealing surface is flat. I had to redo is as the returning company the PO used overtightened the bolts and crushed the gasket.