Do you know what year it is? My ~2004 vintage Ribtec also had a fairly soggy/soft deck in places - they didn't seal the underside of the ply at all at the factory, presumably to save a (very) few pounds and a bit of time...
I had a yard pull the whole deck off last year, and some of the stringers also hadn't been fully sealed and were rotting at the top, and so we ended up doing quite a bit of work to completely make everything good again, and fit a new deck. And this deck has been properly sealed underneath, all cuts in it sealed, and all screw holes sealed!
__________________
|