I have two higher mileage BMW's in the family. When acquired , they needed their valve cover gaskets replaced. The rubber gaskets were quite brittle and, in the worst case, could easily be snapped into pieces. It makes me wonder how the valve stem seals are holding up. I notice on the Amazon site that the first reviewer of this product uses it for preventive maintenance on his cars. Is this a good or bad idea for a car that is running well with little oil consumption? Finally, is the chemistry in ATP AT-205 basically the same as you would find in most high mileage oils?