does anyone know of any 'real' reason why bmw recommends the use of synthetic oil on new cars? i mean, what is wrong with using regular oil, grade optional depending on weather conditions etc. ? please state 'real', meaning, technical reasons for using synthetic, not just because 'it's better', 'voids warranty', i mean what damage could be avoided by using synthetic. also, doing regular oil changes at the usual 4K mile intervals applies. thank you.