verdigris question

[Pppdude@cs.com]

I've come across an old S&S upright which I strongly suspect has a verdigris 
problem, and a very severe one at that.

Basically, each and every key is sluggish, and many do not return at all to 
their resting position after being played.  The instrument is not playable.  
The owner says it just needs "a good cleaning".  I disagree.  I don't think 
humidity is the problem either, since the climate around the piano is not 
extreme, and the owner says the sticking problem does not seem to change with 
the seasons.

I am not a piano technician, so I'm interested to know if there is there is 
an accurate way to diagnose this problem (without calling in a technician), 
and if there are any new and exciting ways to treat this problem that I could 
suggest to the owner.

Does anybody know of any other possible causes of this instrument's misery?