It's for a '92 500SL with 160K. The manual says to use 20W-50 above 32F which is where it will be driven and all the Mercedes dealer service records show it was changed with 20W-50. I would like to use Mobil1 but all I found was that they only go up to 5W-40. Only Valvoline has a 20W-50 synthetic. Is it just as good?