I've had trouble with the right side rear marker light too. Its design is very problematic, the way the bulb is perched in it's clip. Make sure there is good contact.

I later purchased a used bulb housing....and then had the same problem with it.

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62 220sb
67 250S
72 280SE 4.5
74 280C
77 300D
82 240D
85 190E 2.3
86 300E RIP 12/28/09
85 300SD
92 300D 2.5
00 E320 Current
Over 1,000,000 miles in Benzes, Since66

....and a whole passel of BMW 2002 and Tii