OK, I have a 1989 Acura Legend. About 300,000 kms now. I am currently cleaning it with Auto-RX and the engine is now smoother, quieter and a little more torquey on inclines. Right now it does not really consume any oil to speak of runs and idles perfectly. I was thinking of running synthetic (GC) afterwards. With Dino in it, it is running well now. What I want is about another 5 years out of the car. So I got thinking, why bother with Syn? Dino is doing a good job now and it will probably run better after the rinse. With regular oil changes I should be able to make the 5 years again since I'm not burning anything now and am not hard on the engine. So why bother running GC or any other syn since I'm only looking for 5 more.