I have seen rebuild kits with an extra paper gasket which is the same pattern as the diaphragm. My YF2100 does not call for that gasket so I never used it.
I wonder if that gasket would solve an issue such as yours. It is not a paper thin gasket. It would seem to have enough compressive characteristics to compensate for some warpage.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission