You’re obviously burning oil. Like Caddyman said, service the entire PCV system. ok and Nevada are right about the problem likely being internal, like valve seals and rings, but I’d try one more thing. Get the engine good and hot. Change the oil using 5W20. Drive it like you stole it–hard–for a week–and change the oil again. Do this a couple of times and see if you can get some of that sludge/gel to break free. What have you got to lose other than some time and a case of oil?