Our microwave was starting to make an annoying rattle when in use, so my husband decided to take it in to the repair shop to see if they could do anything with it. He came home and said that when they had finished rolling on the floor laughing, they said they would look at it.
Really, it goes very well and has ever since we bought it - which, by my calculation, was around 36 years ago. I think that the problem is that the wheels that rotate the tray are rather worn down, hence the rattle (when it doesn't stick and refuse to turn at all). Everything else works fine. I really don't want to have to buy a new one, which wouldn't last nearly so long.
It's not even our oldest appliance. Our freezer is around 43 years old, and my Kenwood cake mixer is nearly 45 years old - that has been repaired once or twice, but it still works much better than a modern one.
I often read that old fridges and freezers should be upgraded, because they use much more power than a new one. Which is all very well, but how many years would it take to recoup the cost of the new appliance in lowered electricity bills? And what about the extra resources - metal, power, transport etc - involved in making the new one and disposing of the old one? So for the meantime, I am happy with my old faithful collection of kitchen helpers. And I am sincerely hoping that the microwave comes back to us as good as new. I miss it!