The starter on my 245 is most of the time making a screeching noise once the engine starts revving as if one kept the key at the extreme position clockwise for too long, despite the fact that I turn the key anticlockwise as soon as I hear the engine revving.

Could the problem be with the return spring in the solenoid.? On occasions , the solenoid does not engage and a tap with the end of metal rod does the trick
Could these two problems have the same cause in that something prevents the pinion from engaging and disengaging swiftly and smoothly ? Any suggested cure other than changing the starter.