True enough....seems to work.
Also had a recent prob with the fine freq adj...going wonky sometimes and the digital display flashing zeroes.
Turned out not to be the variable capacitor at all...cleaning and reseating the rear brass 'shaft' nut to the (newly cleaned) Alum. housing made a minor improvement.
It was the frequency range selector switch.
Applied Yellow deoxit (low viscosity) to all contacts, exercised the rotation and all is well.
SG503 frequencies working well now...even the amplitudes are solid based on my Scope (calibrated with an SG504). SG504 head calibrated to within 0.15dB.