I've posted about this sporadically. Today was "wiper action day". Lucas in Inverness could not find a replacement listed and suggested I try Land Rover agents McRae & Dick who quoted £84 for a new one. I found an auto electrician, David Riach, at 8 Harbour Road, and asked him where I might find a replacement, possibly off another vehicle. He pointed out that it was probably just seized as rear wipers don't get enough work to wear out and advised taking it apart and cleaning it. He quoted about £60 to repair the LR starter motor -- I gave it to him and considered it cheap return for the free advice.
OK, it's been a wet day. So I stripped the wiper motor down to the basics and cleaned everything including the brushes with WD40, hot water and detergent, rubbing off the rust with an old tooth brush and a pen knife. I just re-assembled it and it works perfectly! Maybe this will help someone else.
Derry