my door lock- unlock don't work. Started getting weak and had to hit buttons several times until it would lock or unlock, I replaced battery's in both rf units and it made no difference, now I have to use the key. Where is the receiver located and are they available to replace? Thank you

 

Carefully disassemble the remotes and use a pencil eraser to clean off the silver colored contact surface pads under the rubber overlay (that you push on to activate the buttons) until they are shiny.

Works wonders.