It's just the distributor caps and rotors. The CEL detects misfire, but cannot identify the obvious.
One more thing: if you wish to just clean the distributor cap, it almost always takes care of everything. But also remember to replace the plugs.
You will see that the plug gap has widened up to 45 and even 50/1,000ths. It should be closer to 28/1,000. When the plug gap opens, it will run just fine at cold start with a rich mixture, but once it defaults to the warm-run state, the leaner mixture will be hard to ignite when the plug gap is too wide.
So: get new plugs, clean the cap and rotor... and everything will be fine.
Be prepared to see quite a mess under the cap... you will wonder how it even ran with all the contamination under the cap.
I have a 93 500 SEL, and it has never seen the inside of a shop for anything other than normal service. It's the best car I have ever owned. It now has 127,000 miles on it, and still drives like new.
I purchased a 93 500SEL in Feb. 2014. Mint condition with 74,000 miles. It's 21 years old and looks and drives like it's newly broken in. In my view the last of the great 20th century Mercedes luxury cars. The look and feel of world class luxury. Totally love it, even more than the 1988 560 SL convertible that I purchased new. I've also owned several 300 series MBs. All were very dependable and great value when purchased used.
I would caution everyone not to have them serviced at a MB dealer. The local dealer here pays his mechanics on commission! The higher the charge to you, the more the mechanic makes! You can't get away without dropping a thousand or two if you go to a MB dealer. It's outrageous. There are usually guys around town who can service them at normal rates.