Bob - sorry to see this factory miss.
Are you saying that the missing nut was causing water to leak? That nut seems more like a retainer to me.
In an only semi related note - Nancy tells me she things the cold water is turned off on our wash macine. Ugh! I was thinking of cutting an access panel in the commode room behind and above the wash machine water hookup box. But I'd rather not have to then place an access panel in the commode room. May just remove the closet door, frame and the dryer to get to the wash machine water hookups - as usual.