For those of you who have to clean under the strings of a grand,
here is a tip.  Take a kitchen Scotch type scratchy pad, rubber
cement it to an 1/8-inch thick board cut so that it is 1/4-inch
smaller all around than the pad (to avoid scratching the finish
with the edge of the wood).  Make small indentations a few places
on the wood side of the unit to give you something to grab onto.

I put some furniture oil on the soundboard for cleaning and
lubrication, I used Milsek but any good oil will work that will
not damage the soundboard.  Use a 1/8-inch steel rod bent with
a handle on one end, and a slight bend (about 15 degrees maybe)
and 1/2 long at the other end to apply pressure.

After "scrubbing" the dirt, clean up with the standard cleaning
steel and a microfiber cloth.  Works great.  Used carefully, the
soundboard looks good and the decal is still intact.

Bob Noble - Noble Piano Services
Mansfield, Ohio