1999 GU 4.2 TD wagon. Engine valve timing adjustment

[nikko]

G'day all,

Have a 1999 GU wagon with 4.2TD engine - 415,000klm. Have adjusted valve timing (tappets) twice - at 150,000klm and 280,000klm. It was hardly worth the exercise because adjustments required were minimal (less than 1 thou).
Have not adjusted since. The engine is running perfectly.
What is the general opinion about valve timing adjustments on the 4.2TD?
I get the feeling this engine will easily run to 800,000klm.
Nikko