I use synthetic in the new car that calls for it. I use dino diesel in the diesels. I use race oil in the race car, and dino oil in the other old cars.
I DONT use synthetic in transmissions or rear ends. Ever!
Edit: "synthetic doesnt cling as well" is exactly what i was told by a friend who ran a one-man rearend shop. He refused to warrantee his work if the customer insisted on synthetic lube. He built Lots of racing nine inch rears.
I have a friend that races stock cars and has been doing it for years. He was gifted 5 gallons of synthetic gear oil so he ran it in his diff. When he tore it down after the season the gears were destroyed. He won't use the stuff even if it is free.
