Since the valve adjustment job is fairly easy but a PITA, why not adust the valves a bit looser than specs, i.e. .005"/.015" instead of .003"/.013". This would throw the timing off a hair, open a little later and close a bit sooner. But will it be significant enough to notice? The benefit being longer intervalls between needed adjustments since they always tend to tighten up.
-- Hans Neureiter, Houston, TX '82 300SD, '95 E300D