It’s possible that the new housing is wired incorrectly. You might try putting the bulb in wrong way round. It won’t turn to lock but may still reach the contacts. do this with the parking lights on. If it changes from high brightness to low, the socket is wired backwards. The fast blink may due to the lower current draw of the parking lamp filament.

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