I forgot to mention that, in addition to regluing obviously loose
ribs back to the soundboard, it is advisable (after the above has
been attended to), to run super-thin cyanoacrylate glue down the
soundboard & rib juncture (leaning the piano accordingly) to attend
to any loose spots that are not readily visible.  (You may be amazed
at how much of the CA glue runs down the soundboard, from behind
the rib!)

Gordon Lee Stelter
Athens, Georgia