D pinblock separation

[A440A at aol.com]

Greetings, 
    I have just looked at a Steinway D, 1974 vintage.  There is a step 
between the bottom of the pinblock and the crosspiece( cornice?) it is supposedly 
dowelled to. The pinblock and crosspiece are flush with one another at each end, 
with a slow rise across the center.   All original, pins are tight, seems 
stable. A few dead bass strings, but the sounding structure seemed good.  
However, I wonder how the block could have done this, under the plate, unless the 
plate bolts are loose, or the plate is bending.  The potential buyers are 
considering a new action, but will have reservations about more repair than that, at 
this time.  
      Anybody live around a piano with this condition and if so, any problems 
showing up?  I didn't touch any plate bolts or screws, so can't say if they 
are loose or not.  
thanks,

Ed Foote RPT 
http://www.uk-piano.org/edfoote/index.html
www.uk-piano.org/edfoote/well_tempered_piano.html