At the last oil change on my 230, I stuck my finger in the drain opening to feel for sludge, after the oil had all drained. Yuk ! Sludge was close to 1/4 in deep. I dropped the pan and cleaned the mess out. Then pulled the valve covers, found the same mess. Cleaned out all I could with fingers and rags, then used brake clean and compressed air. Makes a big mess, but is now squeaky clean. This has to be done BEFORE reinstalling oil pan, or mess is now in the oil pan you just cleaned ! While cleaning the oil pan, I noticed the bottom of the drain opening was higher than the bottom of the oil pan. This allowed the sludge to stay in the pan after all oil was drained. I should mention the drain was on the rear of the pan, not the bottom. I cut a 4 inch square piece from another pan with the drain in the bottom. Then cut a smaller hole in the bottom of my 230 pan. With the patch welded over the opening in my 230 pan, I now have a drain dead center in the bottom, with no lip to retain sludge. After installing pan, I put in 3 qts oil and 2 qts auto trans fluid. No oil filter. Drove car 30 miles, and drained it out. Looked like black paint coming out of pan. Drained and cleaned oil filter canister, installed new filter, added 5 qts Shell Rotella 15-40. Drove the same 30 miles, pulled dipstick, oil looks like it did when I put it in. I highly recommend doing this if you oil turns black shortly after an oil change. That dirt circulating through your engine is not a good thing.