I used to feel the same way you feel now.
I picked up a BLACK - very high quality bathroom hand towel (because of its size), folded it in half, and have had it draped i over the center arm rest for about 2 years. After a week, you'll never notice that it's there. (Blk to match the interior)
I have the clam shell type and it's great! While I was testing cars, I hated the rolling cover for the arm rest! I'm sure Mercedes can sell you the part, or if you want it cheaper you should look on ebay or auto salvage yards.
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