Since my wife's '03 Honda Odyssey requires 5w-20 grade oil, I usually find myself not finding my preferred brand, Mobil 1 0w-20, and I end up buying Motorcraft 5w-20. Some many time I end up switching back and forth between Mobil 1 and Motorcraft oils. Motorcraft is a syn blend, as far as I know. Mobil 1 claims to be compatible with conventional oils, reason for which I haven't worried too much about it. Could this switching back and forth between oil brands/formulations eventually have an adverse effect on engine seals, for example?