Synthetics are supposed to swell seals and gaskets and help stop minor oil leaks if used for several thousand miles. If you have a major oil leak, then you are throwing away your money. Now that I have some of my major leaks fixed, I might switch back to a synthetic. Also all diesels will burn a little bit of oil, I don't care what anyone says. I think now that I got my leaks fixed, it should burn about a quart of oil every 3,000 miles, but I will have to wait and see.