rear wiper problem...

hi have a problem with rear window wiper not turning.

the spines on the inside of the wiper arm have worn smooth(being used in frosty weather maybe?). so when i take the wiper off the spindle turns no bother. however the edges are fairly smooth on the motor too.

will i just get another wiper arm in a scrappy,or does anyone have a quick fix?

thanks.
 
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