You may be able to find a learning remote that can copy the signal from the old one.
What usually fails on a remote is the conductive carbon button on the back of the rubber keypad. It connects two sets of metal fingers on a PCB when you push the button.
Sometimes, just taking it apart and cleaning it up will straighten it out. The button starts to fall apart leaving crumbs all over it.
If that doesn't do it, there are kits that you can use to rebuild the conductive button. Caikote 44 is a product to look for.
The third option is to solder a fine wire onto both sides of the fingers and mount a miniature momentary switch on the remote case. Cheap, easy and if there is room on the remote it doesn't even look too bad.
