These sump washers spread the load.
Zinc plated OE sump pan washer.
chgclassics.co.uk
I don’t use cork gaskets as they deform too readily especially if you try the 18ftlb
There are 2 other gaskets a paper one and a thicker card type. A smear of aviation permatex on either side of the gasket and you should be fine. If the tin sump has been dressed flat esp at the bolt holes
I use an ali sump and you don’t have these issues.