Rear wiper

The rear wiper on my 1983 928 isn't working. Motor comes on and it moves back and forth an inch or two but won't travel over the whole window. Any ideas? Easy fix or not?

I slightly adjusted mine once and had no problems afterwards. But not easy to tell your specific problem. I just checked that the motor was solidly attached and not shifting as it runs and that where the blade arm attaches does not have broken teeth etc. Maybe a pic of the area where it works or a video of the sweep might help.