He's right. If they rotten on the outiside they're dust inside. They rot from the inside out where the water from the hood drains out through the sills. The drain holes in the sills get clocked and they fill with water. I've driven one where you could hear it sloshing around.
Best bet is an Eunos over an MX5 as being imports they've generally spent less time in our salty winters.
Nick