Hey you’re almost there… I’d start by checking the easy ones, the rear light assemblies. Do you see how to get at the bulbs you want to check? Often, to break the corrosion, all it takes is the friction of unscrewing and then re-screwing the bulb. I try to use a clean, soft cloth to keep my greasy prints off the bulbs.

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Michael

1988 300 SL (5 Speed)
1994 E320 Wagon
1997 C230