if you do an oil analysis and i dont have the link anymore, it was an arguement on motorcycle or automotive oils in bikes, that dif oils are made of dif parts when they are analyzed, some have more ash in them etc, and the manufacturer also knows what properties are in the oils, hence they designed the engine around them. thats what the oems want you to think anyway, the truth is the oems and the oil companys are in cahoots w/ each other, the oem stamps their name on the box and charges more for the same stuff that you get at walmart or autozoo or whereever. in the case of motorcycle oils there is a dif in that there is a moly clutch additive in them cuz the engine oil is the clutch and tranny/gearbox oil as well. the local ford dealer stocks castrol, wouldnt surprise me if motorcraft oil is castrol, as it is the only other lube recommended by ford. chevy/acdelco oil is mobil1 synthetic, thats why the oil change light is programmed for 10k miles. thats why the dealers have a ready supply of the other incase they run out of the regular high dollar oil. honda gn4 used to be castrol but switched to mobil mineral oil (clean 5000) w/ the clutch additive and runs it for 4k miles and filter changed every other change (8k) i personally stick to the ole harley method of changing oil on bikes and thats oil and filter every 2k cuz of the extra strain on a bike engine. my trk gets castrol, i used to use purolator but since i have no access to those filters readily here im forced to use fram. ive used valvoline and other brands, basically what im saying is use what your going to use and have been using, unless somebody can prove to me that there is a best, i dont really see too much of a difference.