Thanks Karlcole,
I think you are right, I will try to find a replacement from a breakers yard
can I remove that mechanism without taking the seat out? If so I may test the theory by swapping the parts with working passenger seat. That way I will know for sure.

Appreciate the help

 

Unfortunately you have to take the seat out which isn't that difficult. However, getting the mechanism out wasn't that easy and it's even more difficult getting it back in. Here's a couple more pics that may help.

 

Hi karlcole, don't suppose you have a part number and/or part description for the housing and plastic wheel?
thanks
hughm

 

The part # for the left worm gear is 7L0959111. Ebay has 'em for $35+.