I tend to top off with whatever I have laying around, does that make me a bad person?
Let's say I buy a five quart jug of Mobil 1 and my car takes five quarts. I'm not going to go out and buy the $8 dollar individual quarts of Mobil 1 just so I can top off between a 6,000 mile oil change interval. If there's a quart of NAPA whatever...or Castrol whatever...etc, etc,etc...I'll throw that in there if it's the correct weight. I know ideally it'd be "best" to top off with the exact thing the original fill is, but what harm am I doing adding a half a quart of whatever at say 4,000 miles into an oil change interval? I mean what exactly IS that oil at that point once it's been thoroughly mixed with carbon, fuel, dirt, and byproducts of combustion? It's not the same stuff that poured out of that five quart pretty Mobil 1 jug anyway. And it sure beats letting the thing run low on oil like millions of cars on the road are doing every day.