I just purchased an SRT roadster from a private party and found a receipt from an oil change shop that shows synthetic 5-30 was used. This was not an oil change done at the dealer. It took place 2 1/2 months ago and 3,000 miles ago. Will I be ok with this different rated oil, or change it out ASAP with Mobil 0-40? I live in Las Vegas and it's still very hot here. Thanks.