Left a residue, not sure why, WD-40 company still hasn't replied
I was cleaning a Yamaha keyboard - specifically the computer board above the keys.  The keyboard was very dirty and all the E keys had stopped playing as well as the B flat keys.  I followed a Youtube video right down to the money.  Everything was going great until this sticky white residue started appearing.  I freaked out thinking I had ruined the keyboard.  However, I continued to use it, wipe it off with a micro cloth and got about 90% off.  The keyboard works fine, apparently the welds will put off this white residue, but it had me scared to death.
Rating: 4 stars