Over-filling the engine oil can cause excessive crankcase pressure, and force leaks. Plain and simple. The leaks won't occur on the pressurized side, though. Valve covers, crankshaft seals, filler caps, etc., are where the leaks will be noticed.

I can remember a few instances when MB "unofficially" recommended reducing engine oil level by about 1/2 quart, but it didn't have anything to do with external leaks. The issue was foaming of the oil in the sump. I remember fixing a few OM602's and 603's that developed valve taps after a highway run. At higher RPM, the turbulence caused by the rotating crankshaft would actually aerate the oil. If the engine was left idling, the valve tap went away after a minute or two. In this case, the oil level reduction fixed the problem.

In the case of the M104 cam adjuster leak, I'd recommend cleaning it thoroughly and watching it closely. Either the sealant between the magnet and the front cylinder head cover has failed, or, the oil is leaking out of the two-pin electrical connector. IMHO, the latter is most likely the problem and the magnet will need to be replaced.