I have an older Panasonic Microwave oven (model NN-ST680S). Other then the light not working (and the replaced light failing after a few days!), the unit has worked well until recently.
One of the roller wheels on the the oven decided to come off recently – and after popping it back, it kept on coming off. After tossing up whether to get a replacement ring for about 1/10th the cost of replacing the new oven or ditching the oven I came up with a better idea. My first attempts at fixing the ring failed, but I worked out a simple, elegant and fairly professional looking solution.
I simply popped the wheel off the ring, cut a roughly 5mm piece of heat shrink tubing and popped it on the end of the ring, then heated it up to cling to the tip. Once that was complete I simply popped the ring back on (with a nice amount of resistance), and it works beautifully and looks good.
The heat Shrink tubing I used (I only had blue – I imagine white would have looked even more professional, but this is what I had on hand) was KUHS-225G. The inside diameter was not mentioned but I believe it would have been 6mm. I posit that any 6-8mm diameter heat shrink tubing would work fine.
Subsequent to doing this I did manage to find a youtube video which showed another solution. The solution was to fashion a washer from a used microwaveable plastic container and use that to hold the ring in place. This may be a better option if you cant get your hands on heat-shrink tubing, although I am very happy with my result.