Having just repaired my 2008 Ford Explorer XLT rear window wiper motor I thought I would share the experience. After removing the motor which anyone can do with a little mechanical ability, I took it apart, several torc screws. The shaft was corroded enough that it wouldn't move. By tapping out the wiper arm shaft with a brass hammer I was able to burnish the inside with the right size tool. You probably could do it with a slightly smaller drill bit wrapped with emory paper. I then coated the shaft with graphite grease and reassembled. Take care to note the gear location and matching teeth of the wiper arm assembly. Price for a new one is around $100.00. With a little patience you can fix your own