New to CL420 ownership and new to the forum so please bear with me. The CL420 in question is a 1997 model that has covered 84,000 from new and during the last four years it has covered in the region of 1000 miles a year. I have seen similar threads concerning disintegration of the oil feed pipe to the tappits and will investigate however my first course of action was to flush the engine with a Wurth engine flush and fill with a premium 5w40 fully synthetic oil. This quietened the noise considerably although it's still irritating with all windows and roof open which is how I like to drive (weather permitting). However I noticed in the service history that it has been filled (by Merc) with Duckhams initially and then with Shell Helix and am wondering if my choice of oil was wrong. Also, is MB the only source of valve gear if replacement parts are needed? Thanks in anticipation.