Quote Originally Posted by 89Vette View Post
It would be reasonable to assume that units still running well -- and w/o any lower ring issues -- will be aging to the point where valve seals will seep (especially at start-up). Take a good look out the back window at (cold) start-up. If you see some [light-bluish] smoke, that's probably where your oil is going.

MMO definitely won't help that. Not really convinced these high-mileage oils would provide the "magic" seal conditioner that would help valve seals either. Seems they're more for simple leaky gaskets -- which are better off replaced.
My rear main seal started leaking so I changed to high-mileage Mobil1 with seal conditioner, and low and behold it worked like a charm 15K miles ago. Still going strong.....