In Aussie manual too? Or the global market manual. Isn't 10w30w just a general recommendation for the cars that have to survive cold weather starts and some summers? Australian winters are mild and don't require that thin IMO. Also our cars are getting on in age, the tolerances in the engine are getting bigger too, I run a 15w40 or 20w50 for most of my old jap clappers, unless the car is newer (less than 15 years or under 150,000kms) then I stick to whatever the manual says.