I want to take my sending unit out that I installed 6 years so I can check to see how much gas is actually left when the gauge reads empty (like it is now) before I refuel.

The gasket/seal is listed as N/A. As I remember it was a rubber gasket.

If I make a cork gasket will it last? It’s the standard 5 hole circle sending unit.

cork used to be standard, cork plus a little gasoline resistant sealer should work well

Livorsi senders use a cork gasket, so you should be fine making one yourself.

I prefer the rubber. You can find them. I just googled and found one on shootandhunt.com catalog for 8.73.

There was also one being made by Tempo.

I like the actual rubber gasket kit because it comes with the screws that have sealant near the shank of the screw which crushes slightly making up for any slop or gap where the screws meet the top of the sending unit. Huge bonus.
Also... the rubber has a staple in it. I assume that this staple.... having no other reason to live... acts as a bond between the ground of the tank and the top of the sending unit.
Might be worth a lil search and a few bucks to get a legit gasket and have no questions whether the one that you engineer from cork is completely sealed.

No matter what you decide. Good luck. I have done that job many times. Hope for a cool day and a nice breeze.