How can I fix my electric door Mirror (Honda CRV Exec 2005)?

If I operate the fold back door mirror button, both mirrors fold back beyond the stop point. It's a devil of a job to stop it once it's done, everytime the ignition key is turned they fold back. and I have to get out and manually push them back to the correct position.
I suspect both mirrors have been knocked before I bought the vehicle and perhaps damaged a locating peg of some sort inside.
Can I repair this myself or is it a case of New units?