I've been using Shell t6 5w-40 full synthetic oil . I'm thinking of changing to Delvac 1300 15w-40. The reason I want to change is never I've done some research on best motor oil and the delvac has some great reviews. The Shell T6 has snaptube vidmate been okay but seems not to last long when my oil change interval gets to 20 %. So just wanted to know y'all oil use and which one of these y'all would prefer?