Grand Banks is probably not what you want if you are interested in minimal maintenance. We have owned a GB for 16 years now, and while it is a great boat, well built, and ideally suited for the kind of coastal and inside waters cruising that we do in the Pacific Northwest, it is in no way, shape, or form "low maintenance."
Even the newer ones, with a minimum of external teak, require more work to keep them in good shape that other makes of a similar vintage and style.
An older one, like ours with its rainforest of external teak trim, teak deck, and wood interior (all GBs have wood interiors) is an ongoing project the moment you take possession.
They are great boats, but only if you have the time, interest, tools and skills, or the money to hire people with the time, interest, tools and skills, to maintain them properly.
Grand Banks can be had with one or two engines, although most of the models from 42 feet up are twin engine. We have a twin, and after owning a twin for 16 years I can say we will never own a boat with less than two engines. There's nothing "wrong" with single engine boats. We just have our reasons for prefering multiple engines under the floor.
If you want more information about GBs, I suggest you join the Grand Banks owners forum.
http://www.grandbanksowners.com/index.php You can get answers to virtually any question you might have about these boats from people who have a ton of experience operating, maintaining, and repairing them.
Fuel contamination does not seem to be an issue in this area. The fuel from the suppliers along the coast seems to be very good. I have never personally heard of anyone having an engine problem due to bad fuel in this area. All the engine shutdowns I am aware of, including our own, have had mostly to do with cooling problems, either the raw water side or the coolant side.
It's certainly possible if a boat has dirty fuel tanks the filters could clog and starve the engine of fuel, particularly if rough water stirs up sludge from the bottom of a tank. But nobody I know personally with a boat, power or sail, has any sort of fuel polishing system on it. And none of them have ever had a fuel-related engine shutdown (I don't count running out of fuel).