There are a couple other things that might be done to help the
condition. First see if the balance rail bushings need to be eased
(being to tight on the balance pin). If the key does not fall on
its own after the front of the key is lifted about a half inch,
try easing the bushing.

The balance rail pins might also need to be polished and a lubricant
applied to the balance rail bushings. This is often a problem with
older pianos.

Larry Richards