Sticky ebony keytops revisited

[Bec and John]

Hi,

For those who may remember my postings a while back on my ebony keys 
being sticky when the weather is humid, I have some more on that issue. 
I did end up sanding them, which improved the situation quite a bit. 
However, there are still some issues.

For one, I've been noticing small black "chips" that show up on the 
ivory keys while I'm playing. They blow off, so it's not an issue. But 
I'm confused how after all this time I'm still getting them, and 
wondering what caused them in the first place (I don't recall seeing 
them before sanding).

When I clean the ebony keys with a damp cloth, it is still is picking 
up something from the keys - the cloth becomes a very light brown after 
going over only half the keys.

I'm afraid to keep sanding them since I don't want to sand too much of 
the key away. Is a better solution to just replace them? Is the quality 
of ebony nowadays as good as when the piano was made (1925)?

Thanks.

- John