My preference for VW 502.00 oils has always been Castrol 0w40. Having said that, our Jetta was at the dealership yesterday to get some things checked out, and I went ahead and had the 60K mile service done (even though we are only at 47K) since our service plan expires next month. Anyway, they use Castrol Professional 5w40. Is it worth changing back to Castrol 0w40 or should I just leave it in?