The original question being also about intervals, I have one comment more for the casual observers than for you JJ.  Dai's "annual" adjustment is convenient, but only allowed if your annual mileage is less than 12,000 mi, or 20,000 km.  The diesel being a compression ignition engine, valve timing is even more importnt than it is with a petrol engine, and the big effect of clearances is on valve timing.  If the gaps are small, valves are open earlier and later than they should be.  If the gaps are big, they're not open long enough.  Either results in sub-optimal compression.  And if the gaps aren't even across all cylinders, the cylinders generate uneven power leading to more vibration and more stress on all the internal parts.

Just like when some manufacturers tell you that you can get away with a 5000 mile oil change interval, but should use a 3000 mile interval if your engine sees "severe service conditions", the valve clearance adjustment interval in the manual should be considered the maximum allowable interval.  If you often run the engine hard, you should reduce the valve clearance inspection interval.  I do mine every 10,000 miles (works out to twice a year) because I ask a lot of this thing, charging up and down the mountain every day.

I got my wrench set from Performance Parts.  Good quality (Hazet?) tools at a fraction of the MB price.  Having those wrenches makes it lots easier and easier means more likely to be right when you can focus on the clarances, not on how you'll make due with less than optimal tools.

-Dave G.