As heavy as the cord is, should be a metal gear......not surprised that it's plastic, but should be metal....hope you are able to find one......a side not, the other responders did to seem to have a problem with the gear, while you have. Possibly there is an issue with unit or maybe you are doing something different.
I don't have a reel for mine, I'm too cheap and don't think one would work on our 4270. The only thing I hate about the power cord is it gets a bit dirty......one thing that comes to mind....are you trying to keep it cleaner by giving it enough resistance to keep the cord off the ground while it is wound in....that would put the mechanism under a pretty good amount of stress.