but it was at a marine engine parts supplier and I know that a few of the boats in Newport Beach still use Detroits.
That explains it. Anything having to do with marine or aviation parts or service will always cost more than the same thing at a car-parts place. And pretty much anything in Newport Beach will cost more than in Costa Mesa.
It's partly an issue of higher rents / taxes near the harbor / airport, and partly a matter of having to buy stuff for stock which they MUST have on hand, but which might not be sold for a while. The prices on everything go up to cover their out-of-pocket for stuff that has to sit.
There are a number of major oil distributors in Orange County, so let your fingers do the walking.