Clearly, a clean turntable is better than a dirty one!
The most important parts to clean are the motor spindle and the sub-platter’s rim, where the belt had been riding without having been ever replaced, maybe for decades. You can use cotton swabs for digital sensors and alcohol to clean the plastic motor spindle. Often, a layer of grease has been deposited:
Dust has deposited inside the top of the motor spindle and greasy stains appear on the bottom section, where the belt rides during 33 RPM playback. Note: a motor spindle should rotate with no noise or wobble. A wobbly spindle is a bad sign: it could have been hit somehow and the vertical metal shaft has bee undeformed. Attempts to straighten it back are seldom successful – it might be necessary to replace the entire spindle if not the whole motor.
The motor pulley can be disassembled so to better access the spindle for oiling and to thoroughly clean each part in an ultrasound cleaner.
You are dealing with 40+ years old beautiful turntables. They deserve to return shiny as they originally were. Decades of dirt deposits may have hidden the original beauty of your turntable. If you happened to find one in your repository or at a flea market, chances are that it is covered with dirt.
You can use common bees wax and a wood preserving oil for cleaning the wooden plinth.
The top plate and the knobs, as well as the outer parts of knobs, tonearm, headshell, top plate, platter and sub-platter can be cleaned with a soft cloth and a special fluid suited for technical hardware.
More delicate parts can be cleaned with cotton swabs used for digital cameras sensors and alcohol. Electronic contacts like the one in the headshell and the relevant leads or those within the plinth can be cleaned with deoxidizing fluid.
Smaller parts like knobs, screws, counterweight, headshell, could be cleaned in ultrasound cleaner available for cheap.