Possible brake caliper leak?

[CFinVancouver]

I was changing over to winter rims on our 2021 model Y rwd and noticed the mess inside the rim. This summer set of rims has been on since March 2023, so 7 months. In that time it looks like something leaked from somewhere. It looks dried, some sort of fluid. I have little experience with brake fluid, but that would be my guess. No issue with the car up to this point, I have not touched these brakes for any kind of maintainence, it has only 17000km. I go regular maintainance on our 2015 model S, but have never seen this. Funny thing is there is little if any evidence of a leak on the brake assembly. I need to check the reservoir to see if there is a loss. Perhaps still under warranty.
Any thoughts? Thx.

 

[Sai Ko]

Check the reservoir first and did you feel anything wrong with brake pedal like squishy pedal? If not may be check wheel by washing it with wheel cleaner. Brake fluid will eat the paint so can't say from pictures alone