MOT failure - Windscreen wipers

My Defender has just failed the MOT on the wipers. There is too much play in the mechanism so the arm is not covering enough of the windscreen (only the drivers side).

Just had a look and the movement seems to be the adapter that the arm itself fits onto. There's what looks to be a grub screw on the side but this is corroded. Is it possible to replace this part?

Think this is it:


I'll go and have another go at that screw on the side.

probably more like this....

http://i266.photobucket.com/albums/ii264/bustersbus/Wiperwheelbox.jpg

or have a look here...

http://www.landyzone.co.uk/lz/f7/wiper-wheel-box-46700.html?highlight=wiper+wheel+box

All sorted now. Took the adapter off and cleaned a bit of corrosion off the shaft. Put adapter back on nice and tight and all seems ok