A lot of guys with M119 engines look at the cam oiler tubes.
They are made of plastic and either crack or fall of.
The replacement tubes are metal.
There is a lot of discussion of this on the forum
Do a search for "cam oiler tubes" or "cam oil tubes" and you'll find a lot to read. There are even detailed pictures posted in some of the threads.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".