Thanks for the reply. This helps a great deal!! This one has a metal (or maybe it is plastic???) safety button, but slightly different from your description. This safety has two parts where the button has a thin metal slide underneath the ridged button. It still has the "sort of C-shaped" metal device hanging down to the firing mechanism, to which the screw attaches through the button. The slide has 5 holes. The middle one is for the screw and the other two at each end allow the "snap to" transition to either on or off position. The snap to is achieved by a captive spring mounted ball bearing, which allows the thin slide to move from one hole to the other. The captive spring loaded ball bearing doesn't seem to be able to come loose, so all I can do to it is clean it by vigorous wiping.
Cleaning it did the trick. It is still a bit firm for his finger/thumb strength, but better this than too loose. And I did get a response from Mossberg. The are sending me a manual. In the interim, I did go back and search their site again and found the book online at
http://www.mossberg.com/selectmanuals.htm I knew it should be there, but it was too late last night.