Search the archives of the Pianotech list at the ptg.org website.  There
is a considerable amount of information in there about "vertigris."

The bottom line is that, to date, no one has found a way to permanently
eliminate its reoccurrence.  Everything under the sun has been tried.
Even rebushing does not work because the wood has been affected and it
migrates back into the felt.  Certain petroleum based products have
been known to cause increased sluggishness over time by turning the
green into a gummy sludge, compounding the problem.

Periodic lubrication has been helpful in maintaining operation of a few
actions but does not totally eliminate its effect in regards to increased
friction.  The only solution found has been to replace the parts.

Regards,
Jon Page, piano technician
Harwich Port, Cape Cod, Mass.
http://www.stanwoodpiano.com/