2007 yz450. been using amsoil 10w40 since breakin but nobody sells it here anymore. yamaha dealer is tellin me to use his kawi S4 cuz its cheap and just as good since they dont deal amsoil. the rest of the shops have 20w50 and tell me to use it instead. but i think thats a bit heavy....specially with the colder temps rolling in here lately and fall fast approaching. its either i buy some 20w50 or kawasaki s4 for the next week until i get to the city, or not change my oil for a few more rides. but it still looks decent. thoughts?