Hello, Mr. Wash recently costs the 10W 40 oil just as much as the 15W 40 oil when changing oil. Why is that so nobody could explain to me but they wanted to convince me to take the better oil at the same price because of cleaning effect etc. I once learned that one does not change the oil class in old cars because the additives can dissolve deposits and similar in the engine and then the engine starts to clap? What is right? Change to the better oil or continue driving 15W 40? I drive a 200 petrol Bj 1983 with approx. 190,000 kilometers. Thanks for your tips!