Hmm oil analysis not showing anything out of the ordinary, but high consuption. Obviously the first thought is that your oil is thinning out of grade or there is a volitility problem of some sort.
Without actually seeing the oil reports, this is a random guess work...but, I wonder if you had reports that would show viscosity at 40 and 100 C? Did it change over the interval?
Since the consuption problem was stopped by frequent oil changes, it seems unlikely, valve guide seal leaks are the typically cause for high oil burning that doesn't raise any red flags on oil analysis (in my experence).