I have a 1990 BMW 325 which I recently bought. I changed from whatever nameless dino oil to Amsoil 10w/30. Being obsessive/compulsive about both tires and oil I immediately started to rethink the choice of oil. I emailed Amsoil for reassurance about using a low viscosity oil in a car calling for 20w/50 and received only a link to their 20w/50 product! This despite the website recommendation of 0w/30 and 5w/20 for my car. Now confused and a bit disappointed in Amsoil, I emailed Redline and they recommended I use 10w/40 in my car, 30w oil being to low in viscosity for my application. I must admit I am intrigued by the seemingly fetishistic allure GC has on thid board, but is it right for my older M20 six cylinder engine? Thanks, Ken E.