This sadly adds nothing, David, but it seems MCC gave the name Leader to a whole range of trucks rather than just one model.
I have beaten Google to death and cannot come up with any Estonian Military history site that is helpful
Somewhere in the cellar I may have some old Morris materiel, civilian, and I am just now going down there to have a look.
At least it is now finally autumn here and there are not so many bloody spiders down there.
Bill