Ulli, Being it that both of your cars have gasoline engines, I don't know why your oil would be "black" that quick. If it were diesel that would be normal due to the carbon. How is you sel running? Maybe your engine is running too rich, how is your fuel economy?
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section