I hope this helps someone.

Very nice PSA Javier.    I found the same thing on my Air 2S.  I cleaned the shafts using a micro-dab of denatured alcohol making sure none got inside the  motor windings.  

Hey, thanks mate. After watching your video, I checked my Mavic 3 and there it was, very little rust but it was there. I am cleaning it out with a microfibre cloth and using earbuds and an electronic cleaner called penetrate

It was small, but I found it with me too. Thank you for the information.

Happy new year 2023 everyone!

Thanks,   I will check mine too.

Thanks for the tip! I'll check my Mini2.

I took a close look at everything on my Magic 3 and can't find any traces of rust.....

I'm wondering if this is really rust.
There was a discussion about a similar phenomenon years ago on a Phantom 4 Pro thread.
I think it was some kind of abrasion from the motors. Not sure.

There is this 'Pantomrain' guy who sells wetsuits for drones and he claims you can fly these DJI brushless motors in pouring rain.
If that is true - rust shouldn't occur no matter what.