I cleaned the slide pots over a year ago, so any traces of contact cleaner have long since evaporated. I am concerned that some of the cleaner might have gotten onto a circuit board and shorted out a component, say a transistor. Since the stereo indicator doesn't light on stereo stations, I'm thinking I might have damaged the stereo decoder IC as well, by virtue of shorting out several pins. What puzzles me is why the AM section still works as well as it does, and why I also lost the pilot light on the slide-rule radio dial (but not the clock display) when the FM all but went silent. Could there have been a short across a transistor or the MPX decoder and the power supply to the pilot light, or a short that damaged a regulator transistor?
I do not have a service manual or a schematic for this radio, so will have to look on eBay. Until I do have at least a schematic, I don't want to poke around inside the set and make things any worse than they are now.
BTW, the H480W radio is indeed solid-state, with most of the set on a PC board. To the best of my knowledge and belief, Zenith never made a tube-type stereo-FM clock radio.