I have a 2008 LC5 Invincible with 90,000 on the clock. A couple of days ago I got into difficulties on a wet grass slope with a 1 ton trailer on the back. I was in low with the diff lock activated. Bystanders later told me that the nearside wheels (top of the slope) were spinning while the offside wheels (bottom of the slope) were stationary. I had to get towed off by a tractor as I wasn't going anywhere fast! I thought the LC5 had electronic limited slip rear diff lock and optional fixed transfer box lock (locked) so I cannot understand why the nearside wheels were just spinning and the limited slip did not activate? Is it speed related - I kept the revs low and power off? How can I check to see if it is working correctly? If it is caput how much to fix it and is there a better system for the same sort of money?