You could also have a small head gasket leak. My now retired '92 300E , for the last 130,000 miles leaked oil and coolant at a slow rate. Oil would go from mid-point on the stick to add oil light in roughly 400 to 600 miles. I identified the leak point early on. It is 2/3 rds back on the passenger side.
I could lie under there and watch it. I elected to simply add oil and coolant as needed. Car is now at 245K and running beautifully.

In my case there was no cross contamination between oil and coolant. Now you would suspect that there would be oil on the ground and oil in the belly pan, but that was not the case. The oil leak was caught in the air flow and swept backwards coating the bell housing and the transmission area.

So jack securely with floor jack and jack stands, remove belly pan and crawl under there with a flashlight. Look around and try to find the leak. If you don't have the tools or equipment to safely do this, then take it to a MB shop.

From the sound of your post, it may be best to simply take it to a shop as the fix is likely to be fairly difficult anyway. As previously posted, valve seals, front timing cover, or head gasket leak.

Steve

Steve