Was away for a few days and just saw this reply. Yeah, brake fluid is super corrosive, especially on glass. The DOT rating (3, 4, 5, etc.) doesn’t play a role in how corrosive it is, it’s more about the different additives and composition of the specific fluid and what it’s service life is. The more you know…

Brake fluid would etch the glass of the lenses. Cleaning the surface wouldn’t return the camera to service. Better than paint would be any other substance to thin out the brake fluid for application, particularly if it were less noticeable than paint. That would cause the repair order to come in from lost data collection rather than a report of vandalism, denying them creeping time and that sweet, sweet data. Definitely don’t do that.