I had a similar problem on my previous boat (R27)—where the buttons on the Jabsco control pad stopped working one by one. I contacted Jabsco before the last button stopped working, who recommended that I replace the control pad and the control box (parts available in kit D-- Part Number 58029-1000). During the install of the new control pad, I discovered that the cable connection (between the control panel and the control box) had quite a bit of corrosion as moisture had seeped under the black heat shrink that was supposed to protect it. After I connected the new control pad cable to the old control box cable, everything started working properly.
So, I would recommend that you check the cable connection (which is similar to a phone line jack) to see if there is any corrosion that could be cleaned off before resorting to anything more drastic. On my R27, this connection was right behind the toilet and was relatively easy to reach. You will probably need to remove the black heat shrink to see what is underneath.
If you do need to replace the control pad itself, it is a bit of a bear to run the cable from the vanity back to the toilet—I had to remove the stove and use my boat hook to pull it through as I recall. Also, if you find that you actually need a new control box, I’d be happy to donate mine to the cause as I have a new boat with a different toilet.
Good Luck!