I am very happy to report that 700 miles on Pennzoil Long Life 15W-40 has completely stopped 3 oil leaks in my 84 Mercedes 300D. The leaks were from the rear main seal, turbo return line, and the oil pan. Prior to putting the Pennzoil in, I ran 500 miles with a quart of Rislone added(this may have helped clean the seals, I don't know). The previous 4 OCI's were with P.C. Duron 5W-40. Leaks were becoming progressively worse on the Duron.