I,ve never ran across a recalcitrant collor that could not be remove by grasping with a quality pair of vice grips and rotating a few degrees back and forth while pulling. Even if whoever had filed a flat on the axle they can always be rotated a bit and the ones where they did not bother with the flat will pull off easy with a 360 rotation.

Having said that before you replace give some thought to trying this. Slide the wheel on and cut a circle of paper card stock about three eights diameter and push on the axle to make an impression. Cut the hole out with a blade for a tight push on fit over the axle and slide tight aginst the wheel and slide on a small washer the fit is not critical. Just solder this with a 140 watt or better iron and acid core solder with a dab of paste flux. When cool just cut out the paper which protects the wheel even it it is plastic and provides the proper lateral fit.

Try this and you will never endure the walk of shame to retreve an airplane that has lost a wheel. This method is far more reliable than any set screw type collor even with a filed flat on the axle. Once first done it very easy to replace a wheel for whatever reason in just a few minutes with an iron.

John