I have a 96 Toyota Avalon with the 3.0L V6 engine, it had over 150K miles on it. I have been using GTX HM oil on it for the last 3 oil changes, total miles driven is about 16K. On the last (the 4th) oil change a little over a month ago. I got a hold of some old Havoline 5W30 oil (not the DS) for...