my LT1 doesnt have the dreaded intake oil leak. i dont want it to, thats why i dont use synthetic. on my turbo 5.0 when i switched to castrol 5w50 it started leaking, but after 5 years the bearings in the turbonetics 60-1 were still like new. i have a 1989 dodge dynasty that uses castrol 5w50 and has leaked since i put the castrol in at 3000 miles for the first oil change after my mom bought the car new. the car has over 500K miles on it now. i just change the castrol out every 5K miles. the car has never been driven hard, so i just keep using the 5w50. if i were to go to a synthetic in the Z id probably go to a mobil 1 15w50