The momentary leak suggests the caliper bore is less than perfect. The fact that presently the caliper has no leaks suggests the seal is riding on a good surface. How many miles/years are on the caliper?

Or, maybe the piston was momentarily overextended, allowing for fluid to escape, suggesting a non-problem.

Try "standing" on the brakes while the car is stopped to check if the pedal creeps to the floor and to check for leakage at the calipers. Does the car pull to one side during firm stops (hands off the wheel)?

I guess the sure thing to do is to disassemble the calipers and examine the piston/bore for any corrosion, pitting, or other defects.

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95 E320 Cabriolet, 169K