Rear wiper problem
Mark,
I had a similar problem, and the cause is the main wiper shaft had corroded badly due to water ingress. This caused the shaft to expand and slow the motor down eventually sticking. I took the motor out and separated it from the linkage and stripped it the linkage completely. I cleaned the shaft using some emery paper and rebuilt it, it works fine now. If you are reasonably mechanically competent then it should be an easy job. When you take the rear boot inner plastic panel off make sure you replace the plastic retaining clips otherwise they will rattle. The price of a new one is about £40.
i hope this helps
Sandro