[masraum]

Originally Posted by john70t

One possibility is pad wear.
The pad thins, the pistons extend, then more fluid is taken from the reservoir.
Organics (vs metallic) wear faster afaik and I thought easier on the rotors. Could be wrong. BMW wheels are always dirty.

Other possibility might be inside the brake booster.

Yep, as the pads wear and the pistons extend, the fluid level gets lower because the system volume increases. I didn't mention that because it only gets driven one week a month, but I guess if that week is hard on the brakes...