I currently am at 38,500 mi. and when I first got my car the original owner used 10W30 , but the factory recommends 5W30. So at my mileage now is it best I stick with the 10w30 or go with the 5w30 on my next oil change. And a few ppl told me to never use 5w30 once I hit high mileage like 70k is this true ?