Type of oil used
In an answer to JetForeman question, I have used Castrol GTX and Mobil 1 10W30, 10W40, and 20W50 depending on the season. I got the car with 136 miles and now it has 204 miles. It had this oil consumption problem since I got it. It increased from 1quart/1000 miles to about 1quart/400 miles. Cylinder # 3 used to foul the spark plug every like 3-4 miles. I still have all the spark plugs that I pulled out and will take pictures of all and post. The electrode in one of them was bent possibly due to a worn valve guide.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer