on certain axle type of uk Mitsubishi fd25n axles (not rubber block type) I have had new Mitsubishis delivered with too many shims in the back axle pivot.over time they can creak loudly or even seize up causing the truck to stick in the leaned over position and not be able to rock on the back axle to accommodate camber or potholes. this could be the reason why one wheel is worn more as its been driving mainly on that wheel till it has worn down and now not able to gain traction thus spinning.

jack up the back end and see if the back axle pivots