[2570p] 3 of 4 touchpad buttons not working

[A.j. 16]

Greetings all,

 

After many trusty years of smooth operation, my 2570p touchpad is acting up.  Actually, the touchpad itself works fine -- but 3 of the 4 touchpad mouse buttons have stopped working.  (The top left button still works; the rest do nothing).

 

Any thoughts on how to fix this?  It happened all of a sudden; no drops, or other obvious cause.  I'm comfortable opening up the case, if that helps (and replacing something, if necessary).

Edited August 21, 2018 by A.j.