I've got a microwave oven that's steel throughout, no coating internally or externally. I've had it for many years and it continues to work very well. There's no corrosion inside the microwave (unlike most microwave ovens I've seen, which corrode through the coating surprisingly quickly) but there's surface rusting on the outside in places. I'd like to get rid of it or at least stop it spreading further. That would usually involve chemical processes to remove the rust or convert it to something else (ferric tannate, usually), but I'm wary of doing that with an oven. Even on the outside, since some of the rust is on vents on top that open into the oven (obviously - there'd be no point in them otherwise) and some of the rust is around the frame next to the door. I don't know enough to assess the risk, if any. I could replace it, of course, but I dislike binning stuff that's still useful, even if I have had plenty of value for money from it. The oven was quite expensive, but I've had it for at least 15 years and it still works perfectly apart from the internal light which died a few years back and which I don't care about. I've never found any need to see inside the microwave oven during cooking, so the light is irrelevant to me. So...advice?