I just replaced 9 or so keys on my MBP. I guess I have that lucky body chemistry that erodes the pretty aluminum key coating over time. Now, for relatively cheap, I have happy new keys (although some of the letters have weird additional numbers on them, but I care not). Plus, I also recently bought a silicone keyboard protector (4 years too late, I know) so that my new keys will look new forever.
Goodbye poor old worn out keys… you served me well.
Thank you, laptopkey.com.