When I bought my 1500 and got it home I also had trouble with the differential lock. I went back to the dealer and he told me something to try before they went out to look at it. He said to get a pry bar and hook it under the lever. That it should pull out from the case about a half inch or so against a spring pressure. And then to spray it well with WD40. This worked, it released the mechanism, which had stuck in lock, and allowed the foot pedal to return to unlock when I take my foot off without having to unlock it with my heel.
Give it a try, simple fixes are lots better than hard ones :-)