Our '01 S40 was left with the sunroof open during a downpour by the previous owner. Apparently both front leather seats were soaked. After the storm, the owner (my niece) turned on the seat heaters to dry them. They have been as hard as rocks ever since.

An upholstery guy she spoke with about the rock hard leather told her that if she had let them dry slowly just with the doors open on a sunny/breezy day, they would have stayed soft. Who knows if that's true, but it's all I can offer.

We've tried Lexol to try to soften them up again, but it has done nothing.
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"Differences of opinions should be tolerated, but not if they're too different' - Sharon Craig