I have the Canon 50mm f1.4 which had the common focus issue due to deformed inner focus ring. I have straightened the ring and the lens now had full range of manual focus, but Autofocus cannot find a happy spot, but instead moves back and forth around the correct position a coupled of times and gives up with the red focus square.
I have inspected the autofocus brush and all 3 prongs are making good contact.
Professional service is not available where I live and sending overseas with combined postage approaches the cost of a new lens.
Is the motor assembly responsible for this kind of fault? Or the electronics PCB?
Ordering replacemtent parts seems my only realistic option.