Would it be an absolutely horrible idea to just now start putting synthetic oil in my car if it has 151k miles on it? it's a '93 SI, that smokes pretty bad anyway if I don't put some sort of anti-smoke sludge in it anyway, so I figure-my seals are shot, so why not protect the metal components better and continue to use the anti-smike stuff. I am currently running 10w40 Valvoline MaxLife. Could I switch to Mobil1 synthetic withough screwing up my engine?