Here is the kit:
Rubber Keypad Repair Kit : CW2610
Cleaning should be tried first. Disassemble the remote and you'll find a PC board and a sheet of "rubber buttons". Use alcohol on the PC board - the side where the buttons are.
There will be copper traces where the rubber buttons contact.
The buttons themselves are made of a layer of a conductive elastomer. Sometimes the layer wears away and requires the kit. Wash the buttons with soap and water and displace the water with some alcohol.
Let both pieces dry and re-assemble.
Replacing the remote or getting a universal remote are generally the other options.