I've always used good quality oils but after discovering AMSOIL in Australia I wouldn't use anything else. I recently scored the 200,000 kms in my 06-Subaru and I wanted to upgrade my oil viscosity, so I checked with Greg Mildren and he gave me the best factory options plus his own comprehensive experienced advice which connected with my mechanic background. Thats how I upgraded to 5W-50. Signature Series AMSOIL. The best Full Synthetic you can buy. Now I know I'm protecting my engine every kilometre travelled.