Reason for rotten floor pans ( 1969 / 1970 Mustangs )

Rotten floorpans,

We "all" know that the first 2 generations of mustangs ( 1964 / 1968 ) have often problems with rotting floor pans. Main reason for this is a leaking cowl. Water cant found the way down and gets all the time to rot through the air vent.
But, the 1969 and 1970 Mustang are different. They have 2 airvents and a better protected and coated cowl.
Here are a few pictures of the cowl and the channel. [note: this pic is not perfect... but in this case its not really the best place to take pictures]

The problem is not rotting metal of the cowl and all but bad sealing of the "gasket" between the air inlet and the body. Water can find its way through the sealing and underneath the carpet. The rest seems obvious.

A new floor pan was welded in place and sealed along the sides.

The new gasket  was screwed in but also sealed in with seam sealer.