Hi I just have some observations regarding oil, on my 1976
450sel I have been using castrol for the last 12 years with no problems.
Last December I bought a 1989 300ce where previous owner used Mobil 1, and its still in the engine.
My concerns are that after 3000 km the oil still looks new, while the Castro oil is black after 2000 km.
As I understand it the oil has following main purposes:
1. lube the engine
2. transport dirt to the filter