Thank you! I'm not sure my multimeter is accurate enough to measure the voltage that precisely. But in a fit of desperation I attacked the board with a Q-tip and contact cleaner and sure enough rubbing the bottom right pins of IC18 (right under the coin battery) and R65 fixes the problem, at least temporarily. I'll see how it goes before seeking a more permanent fix (fingers crossed).
BTW the coin battery is not shown on the diagrams in the service manual. Is this because I have a newer board revision? My main board version is KLM-596-8