Mike, pin oaks also have pointy lobes and it is VERY common around here for those trees to have a 40 year lifespan. Our soil doesn't have enough iron in it to support the tree later in its life. The symptoms you describe are not unusual. Whatever the problem, I agree, have the conversation with the neighbor. I don't know how it is where you live but I think in PA you have to have written documentation to your neighbor showing you advised the tree was a problem. It also might be worth calling your insurance company and ask their advice.
