It probably had air in it that worked itself out.

The bleed screw, if there is one, would be on the upper side and above the bearing preload adjustment. It may still have the rubber cover but looks like a brake bleeder.

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120