We bought a Kenwood Chef mixer in 2013, and use it mainly for kneading pasta dough, which is about as much abuse as you can dish out to a mixer. It is still going strong after a decade. It definitely has metal gears. Whether or not they still do, I don't know, but I thought you'd appreciate another brand to research. Not sure how easy they are to find outside of the UK either.

Edit: The only downside of our mixer is the amount of noise it makes.

All these belt posts. Aren't belts low hanging fruit, BIFL-wise? Like, you really have to screw it up for it not to be BIFL. I have two inexpensive leather belts that I got at M&S (department store in the UK) as a teenager, and they're still going strong after 20 years. One has been worn almost daily. I think if it's reasonably thick real leather, it just lasts, regardless of brand and cost.