I'm afraid you need to unsolder a few connections and pull the tuner. This article has some long bits about cleaning & lubricating an RA-113 tuner:
http://antiqueradio.org/DuMontRA-113Television.htm
Start at, "Removing the Tuner."
Every inductuner that I've looked at had considerable petrified grease, etc., inside, so it's a good long-term strategy to clean & re-lube everything, even if the tuner turns at the moment.
Regards,
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html
