Watch out when you tighten a cork gasket.
They squooqe out and break and leak rather easily.
A sealer is always a safe bet, but will make it harder to remove later. It's your car, and your decision.
To bulletproof it for no leaks, clean everything really well and dry, and use a little premium RTV on the gasket, then assemble it and let it cure before filling the trans.
You probably don't NEED it, but it's your call.