Logitech Harmony 600,650,665,700

Instructions PDF: Logitech Harmony 600-700

Do you need Deoxit?
The directional keys, center OK, Volume and Channel use metal snap domes. Those can’t be fixed by ButtonWorx™ pads. You can replace the metal domes but it’s difficult and very rarely needed. Metal domes can be cleaned by pulling back the sticker film and using 90%+ isopropyl alcohol, Deoxit or some other electronics cleaner. 
There is one issue with this model where SOME (not all) just don’t provide enough pressure on the snap domes to activate them easily. That can be the case before or after installing a ButtonWorx™ repair. The OK button is the most affected, then the directionals while the volume and channel are not effected. 

…. It’s caused by slight variations in the manufacturing of the housing and other parts and also can be aggravated by the 0.5mm additional height caused by the ButtonWorx™ membrane. The kit includes a 5-dot sticker for the OK and directionals that will solve the problem of not enough height.  If the buttons are still hard to press then the metal domes need to be cleaned.