I have heard of this before, but I haven't done it. I did my 240D shortly after I bought it and then again 15,000 miles later. All valves were way tight the first time. Several valves were tight the second time, but not by a whole lot. I haven't put enough miles on my 300 to need to do it a second time yet, though its time will come soon (after I get back from the sandbox next year).

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.