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I believe I can help, here is a video for the oil maintenance light reset. https://www.youtube.com/watch?v=1bIFUEQNCFo
You should just be able to select oil grade 229.5 using the + or - buttons on the right side of the steering wheel. Then you just use the left side "page" button to select the oil grade. Don't push the reset button on the oil grade
The video is for an E class but its very similar to your CLK.
Once you get to the type of oil screen, use the "up" arrow on the left side of the steering wheel. Then push and hold the reset button on the left side of the steering wheel.
Here is the actual factory document that states to select the oil grade type (use 229.5 for synthetic). Select the oil grade using the + or - buttons. Then use the "UP" arrow on the left side to confirm.
Here are the exact instructions.