On Wednesday, June 6, 2018 at 4:50:55 AM UTC-7, Ron Hardin wrote:
My Superradio III just died, after being on 24/7
for around 20 years. I think the varactor
governing tuning failed.
My knee-jerk prejudice is that it is a bad electrolytic capacitor.

Next, I would look for RF leakage from the local oscillator. If you do not have a suitable oscilloscope, you could use another radio.

However, if you are right and you do not need to be able to tune other stations, you could replace the varactor with an old-fashioned variable condenser.