Talking to an RF engineer, he said that the nicad batteries died. After 30 years or so, a burned out component has broken loose, separating the battery from the circuit. Now when sunlight hits the panels, it goes straight to the transmitter. When the panels are in the dark, it has no power and forgets everything.
Maybe they got some bad solder, less lead than needed to retard the growth of “hair” from the tin, creating a beneficial short?