My 560 has a 2-part reservior. The back half feeds the rear brakes, and is filled by overfilling the front half and the fluid dribbles over through a small hole near the filler neck. Difficult to see the fluid level there. I spent 2 days trying to bleed the first time i did it, very similar story. Hope it helps.

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Earl McLain
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)