I'm changing the oil and some other fluids in my grandfather's Fleetwood. It's an LT1-powered model with 96,250 senior-citizen-driven miles. Lately it takes 10 mile trips almost every day in Arizona weather. Before the last oil change in November, the car had been sitting for a few weeks at a time since late August, with short drives made on occasion. There aren't any oil leaks that we know of and he doesn't have a brand preference. Should the car end up sitting in the garage again, what oil should I consider?