I had to remove a hinge, and now that I look at it, I can't tell if there is a WMK or not. What I was seeing before was the ink from the locomotive on the back of the stamp. So, sorry if I've raised some curiosity that maybe wasn't warranted.
Fairdinkum, I've seen your site before, and thanks much for asking for the images:


Bobby, I did check out the #97, for Tambo, Queensland, and it's a very rural place. But the examples of the cancels shown were not the same (sun ray cancel), so I don't know if 97 still represents Tambo or not.
Thanks for the suggestion!
Appreciate the responses from all, Ray