I recommend that you get a second opinion from someone well experienced with these engines. Mine leaked for a long time in this area, and I can see where it could easily be mistaken for a headgasket.
I would wash the engine at the car wash in this area. Then keep an eye on it for a few days, I'll bet you will be able to tell at that point.
If it is indeed the upper timing cover, by using a translucent blue sealer that MB sells for this application, you can slide the cover forward without disturbing the seal. I had never done one before and managed to get it sealed up the first time. I attribute my success to the use of this sealant which is perfect for the job.