It’s not my thread, but when working on cars, I use liquid gasket
from a tube, called RTV or Silicon Gasket Sealer. It is available at
any PEP BOYS or other auto parts store, and is amazing stuff for all
sorts of little repairs. I’ve even used it on my refrigerator. It’s
non-toxic too, I think. Just squeeze out of the tube, just like
toothpaste, and then set it and let it dry. It’s rubbery and
cushiony, and available in a blue color or clear. Useful and cheap!
The other option, “Sheet gasket” is like a very durable, hard pressed
cardboard that you can cut into shape, also available at the above
stores for when you can’t find the right gasket to fit your engine
block in your antique auto, and have to cut your own.