The most likely explanation is that your CL55 does indeed require addition of oil. Given that you seem to use a fair bit of its performance capability, this doesn't surprise me.

That said, the electronic sensors do go wonky on occasion, so it may be worth checking the oil level with the dipstick tool to verify the sensor is correct. As others have said, the dipstick is a service tool which cannot be left in place during engine operation. On the 55K engine in my w211 the oil measures 168mm depth when full. I am not certain the same number is valid for your 215, as there is the possibility it utilizes a different sump design.

The factory seemed to frequently alter their view on whether to fit a dipstick or pan sensor, or both, over the last dozen years. The only combination I am aware they did not use was to fit neither.

The 722.6 automatic transmission includes a dipstick tube, but again, the dipstick itself is a service tool. They went so far as to include a red locking pin in the cap in an attempt to avoid the introduction of incorrect fluids.