It's an idiotic design to start with, made with expediency in mind.
Modify it by gluing a very thin piece of aluminum foil(cigarette pack
foil or such)to the bottom of the rubber key where the carbon contact
is/was. Shine up the copper traces, usually in a circular pattern
directly under the rubber key. Use an rubber erasor as others pointed
out. My remotes now work effortlessly...

Tom Gardner wrote:
Is there any way to repair those membrane keyboard switches with the
carbon-like button that makes contact on a PCB? Sometimes cleaning them
works but not always and now I'm in danger of getting MY remote commandeered
due to a faulty remote in somebody else's possession. It seems that there
is a deposit on the PCB that is also affected and the button seems to be
non-conductive anymore.