First, I would lubricate and inspect the motor and gearing. I would use a light oil and needle oiler to oil the output shaft side of the motor bushing, and inspect the gears for splitting or cracks on the shaft. Either of those could make the sound (dry bushing or cracked gear).
Since Lionel no longer carries parts for this item, replacing damaged motors or gears might require detailed descriptions and pictures of the parts (example gear diameter, tooth count, shaft bore size, motor size, and so forth. We would have to then substitute and use 3rd party common "toy" parts such as motors and molded gears to fit and replace the offending broken parts.
The product support page. https://www.lionelsupport.com/Ferris-Wheel
Since no pictures of the motor and gearbox are provided, I can only go off what I know about other similar accessories.
Again, what I do know is this is a "can" DC permanent magnet motor and no you will not be replacing brushes and springs in it.
The voltage regulator board shows us again, this is a DC can motor- I can know that just from this picture alone.
