It is pretty easy to do, it can be done if your patient. Take a pair of diagonal cutters and gently pry the washer off the end of one side of the shaft, keep working around the washer, do not cut it off, you will be reusing it. After you get the washer off, slide the shaft out of the opposite side, remove the broken wheels, install the one new wheel and reinsert the wheel shaft, install the other new wheel. Now, take the washer and put it on a vice or something steel and gently hammer it flat back into shape. Put the opposite side of the shaft, the side that you didn't remove, on top of a vice or something that is steel to support it. Now put the washer back over the chewed up end of the shaft and gently peen the center over onto the washer and it should hold. I have been doing it this way for over 40 years and I have never had an issue.