So I just joined the missing quantity and the dipstick reaches now to the 2nd level with cold engine.
However engine noise is always the same. So I guess I have to take it to the MB shop to get their opinion what is going on.
The check engine light never came up again. So it was one of those 2 big tubes coming lose. No idea how this could happen itself ???
However I had to reset the CEL to get the check engine light off, it did not go away itself.
I will update with more news from the MB shop.....

thanks for all your help and assistance, happy to be part of it.