Could be one channel has failed in the amplifier caused by 40 year old components failing.
Could be a shorted speaker lead, damaging the amplifier.
Job to say without seeing it on the work bench with test gear.
The cueing mechanism should lift and lower the tone arm regardless of whether there is oil in the cylinder or not. The silicon oil is used to dampen the movement. If the lever does not operate the tonearm, then there is mechanical damage under the platter.
Question edited for spelling and add some SPACES!
Did you look for bulging electrolytic capacitors?
If you can't see any, then you need to take it to a service centre, as they have thousands of dollars of test equipment and access to parts.
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To be honest most people simply replace the keyboard than try and fix them. They are not expensive. You could have a problem with the driver for the keyboard, so you could update it. That's worth a try before chucking the keyboard!
