So I have a 07 V star 1300 with 25k miles on it and I live in vegas, in the summer it gets in the 110 range and 30 in the Winter. What kind of oil should I use, I'm not too concerned with brands, I'm thinking amisol or Yamalube (not sure yet, but I've heard good things). But what about grade? My manual says 20w40 but Yamalube doesn't make this grade anymore. I've seen stuff like 20w50 for summer and 10w40 for winter, would this be accurate?