I know this is a Maverick forum but I have a simple oil question. 87 mustang 5.0 40K original vortech V1 super charger gt 40 heads Cobra R intake 70 mm throttle body yada yada almost 20K in motor. I got the car 15 years ago and as memory serves it only ever got 5w20 full synthetic. I can't find my big book O receipts and the car has sat 7 years broken. Now it's fixed and in need of an oil change. last time I got changed my dad had it done at a local walmart before our road trip 8 years ago. I told him full synthetic when he took it in but that doesn't mean anything given some of walmart charging tactics vs whats put in. Am I safe to have full synthetic to be put in this motor still or will I have problems. I know I know it's a mustang, but it is still a 302. I am paranoid as it took me the better part of a decade to get back on the road. any thoughts?