I had the same "DIM" problem on my 84 500SEL. I cleaned the dimmer, cleaned then painted the reflectors silver (spray can from just about anywhere will be fine), and cleaned the prisms. When cleaning the prisms, use mild soap, a soft rag, and don't touch them with bare hands while puting them back in. Replaced the bulbs with 194 type and now have to turn the brightness down as they are too bright if turned up all the way. They have been this way for about 5 years now and I have had no problems. I have modified the car some, but it still looks original in every way. This method keeps the original look which is very classic.
Just my 1 cent worth (my opion isn't worth 2 cents).

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84 500 SEL (307,xxx miles)