VALVE ADJUSTMENT INTERVAL

[jemmah]

I have a 2007 Yaris hatch with 138000 miles. This Yaris has been great other than half-a-dozen headlights each year. I try to do all my own maintenance.
Compression is good all cylinders but it's such a project to check valve lash that the Toyota manual states that valve clearence is checked by a Toyota technician with a stythiscope. I assume having Toyota preform this task would cost me a bundle plus they probably would adjust them whether they needed it or not and there goes the $$$$. I few Yaris owners I spoke to say they never needed a valve adjustment BUT my mileage is higher than most.
I want to know from someone who really knows: What is the point in time where most Yaris's require a valve adjustment. Not a single person I've talked to needed one BUT as we all known this auto had solid lifters and a adjustment should be needed sooner or later. They must be using some serious metal for this area of the engine!!!!
Thanks,
JEM