Hmmmm, I know down here I buy oil in a FIVE QUART jug. Not a gallon jug. You should be able to find that up there, too. I'll stick to "old man thinking" on oil. For the last twenty years, I've been using Castrol 20W 50 in my hotrods. I never had sludge, I never had a problem with seals or wear. I'll stick with that, thank you.
I can say this for certain. It's not as important to change your oil every 3,000 miles, as it is to stay with the same type of oil. Additives in differant oils don't always mix well. Which contributes to sludge build up. That whole 'one odd quart of oil' is bad advice. If you choose to go with Rotella, stay with it. Same for Castrol or whatever brand you use. I see the differance in the engines I tear down all the time. If you go to what ever lube place is having a sale and get whatever they have there, I can almost guarentee that your engine has a least 1/4" of sludge in it. If you change the oil regularly with the same brand, you'll be much better off.
Just my .02