I guess what I'm saying (and being a Quality Engineer in the auto industry, I've run into this a time or two.) Typically when you have an issue, it's not due to the design of the product, otherwise 100% of that product would exhibit the problem. What you run into are manufacturing defects that affect a small percentage of the total product (like what happened with the PCV)

The problem being "fixed" in 2006 doesn't mean they re-designed it, it most likely means they identified the defect condition and corrected that. Thus eliminating the failure (but with the exact same design.)