thanks. i still think it's my driver's side sidemarker socket, b/c i can see lots of green gunk & corrosion on the metal surfaces that contacts the bulb. I tried to squeeze a mini sandpaper in there to clean it out but i can't get rid of all of it.

is there a better way to clean the socket?

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Current cars:
2001 MB E55 AMG
2003 Honda S2000
2000 Honda CRV

Gone but not forgotten:
2004 BMW 325i 5sp sport
1999 BMW 540i sport
1997 MB E420
1995 BMW M3 coupe