To me it looks like you have a problem with one of three things. Wheel bearings or bushings are worn. Wheel axle is worn. Wheel axle is bent. You will need to remove the wheel and check those three things first.
View attachment 63756Maybe, but that is a really big guess, without seeing the axle. I looked up your unit and it looks the axle only comes as a complete assembly. Is your axle assembly cast iron or stamped sheet metal? Are the vertical bushings or bearings in good shape?