The fuel in the oil should be negligible. The fact that it is a lot, that is the main issue.
You or most people may not know this, but the OEM is not much interested in your vehicle's used condition lifespan beyond what they are warrantying. They long ago decided new platinum plugs(existing decades and more before then) were good enough for 100k miles. That was also the time frame when the OEM was pressured by new car companies like Saturn who began with long warrantee periods. Before that, 50k was common, and 60k was the high end. So they increased the warrantee to 100k to match, and then pushed the service intervals to save them some money. That required the platinum plugs and synthetic oil etc.
Bottom line, new technology is great, but the economic forces are the main priority for all companies. Car makers have always used whatever is just "good enough" to last in majority, until the warrantee expires. That means they do not use the best parts, oils etc, unless they have to, again, to reach through the warrantee period. That is why they recommend 10k intervals, for sales purposes, not for best engine lifespan. They are relying on modern oils to survive the extended periods, and bad owners who will go beyond those.
So I do mean to offend if you don't realize the facts, the OEM is not looking out for your best interests, and nor are the dealers. Here on a forum was are unlike them, we care very much for the vehicles and the owners. We strive to make them the best they can be, and that means finding the best parts, and fluids, available.
Dig around online, you will find tons of stories about plugs that are hell to remove, and terribly worn when they finally get changed. The same goes for oil, the change interval is a big subject. The manufacturer only cares that they don't have to spend excessively on service work while under warrantee. Most engines will last 100k miles with 10k oil changes, using OEM recommended oil. I personally don't want my engine to use a quart of oil per month after it's 100k miles old.
To make an engine last as long as possible, use the best oil you can for the money you can afford, regardless of OEM recommendations. They used to use dino oil, and recommended it, for decades after synthetic was available. Stop assuming they care about you, they do only while selling you the vehicle and until they have no liability for it.
Spark plugs, plug wires, oil and many fluids should be changed much more often than OEM tells you to. People get complacent and they forget to do plugs, and never do them, and the 2nd owner finally discovers the problem when they have 150k miles on them. The extended intervals are bad for the vehicles, good for the OEM, and bad for owners after the vehicle is past warrantee of 100k miles. Today's used cars are worse than any were in the past, due to poor maintenance. Too many people believe the OEM and dealer recommendations, as being good for the car and them.
