A wet Miata cabin is almost never a leaking top itself; it is failed weatherstrip or, far more often, blocked drains letting water back up where it should run out. Chase the water in that order and you fix leaks permanently.
Water that gets past the top is supposed to fall into the rain rail behind the seats and exit through the top drains, and past the doors through the door drains. Blockage, not membrane failure, soaks the floors
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