I own a 2001 MB CLK320 convertible. I purchased the vehicle with 101,000 miles. The engine is consuming lots of oil 1qt/500 miles. There are no visible leaks and I have replaced the valve cover gaskets, had the oil changed, and am using Castrol GTX 20W50 in the crankcase. What is the problem? My guess is the valve seals, although I never see any smoke from the tail pipe. What are your thoughts?
If you are using a synth oil try a full mineral oil, this may help, stem seals will often cause a puff of blue smoke on cold start up and clear fairly quickly, check the plugs for signs of oil burning this can look like white or grey deposits on the porcelain or the earth electrode, let me know what you see.