It looks like the valve clearance adjustment is with shims. So how often is the factory setting out of adjustment? Seems like a lot of work to change the adjustment, or am I missing something? Some have stated it is very important to check. Shim adjustment do no seem to change that much, do they? Or the shims hard to find at dealers? Very curious as it seems a major job to check and then adjust with having to pull the timing chain, cams etc.. What is your take and feedback.