Put 10-40 full synthetic in my 87 5000 turbo quattro at 100,000 mi. Put "Charlie" spring and shim in soon after. Synthetic oil stopped the lifter noise, have had NO oil leaks, burns very little oil, starts right up at 10 F and now has 190,000 mi- Only change the oil every 10,000 (filter every 5,000 or so)