I have fitted a reproduced mirror gear set today to test on behalf of a small company in the UK. I have no financial interest here, I just think it's an excellent replacement for the fragile plastic original mirror adjustment gears in the Murena's mirrors. The whole gear assembly has gears of hardened steel, mounted on hardened steel pins attached to alloy carriers. The complete unit fits exactly in place of the plastic gear set and early signs are that it is a much more robust setup. I've wound the adjustments as far as they will go in all directions and folded the mirror in and out, then I took it for a 120 kph run up the motorway and the mirror is as solid as a rock.
It took half an hour to fit from start to finish and so far I haven't found any faults. I believe the supplier plans to offer a 12 month warranty. If you want to know more you can look at their Facebook Page,
https://www.facebook.com/plasticsoupkitchen