FWIW- a brake fluid drop is normal if it's very gradual, and your brake pads are getting worn.
My W124's with fresh pads will start at the max. brake fluid line, and when the front pads are 3/4 worn, it just barely above the minimum mark of the brake fluid resevoir.
If I don't change pads and continue to drive aggressively with only the minimum amount of brake fluid, the "Brake" light comes on intermittantly (same thing happens with the windshield washer resevoir).
1988 360TE AMG