with missing your scheduled OCI.Start buying Fram filters immediatley,and start looking for 70 weight non detergent rerefined engine oil.After these drastic steps you will be able to do an OC with anything laying around in the garage{even topping of with slick 50!!!}Soon you will be able to run 2 qts low with pride,while looking hard at that window sticker that says your 2k overdue.We run Cat C7's on bulk 15w40{dont even know who makes it,I think Fuchs},and miss OCI's all the time.Havent had an oil related failure yet{unless you count pumping it all out on the ground as oil related}.The new Cats dont last long enough to wear out,so its probably not a fair comparison!!!