I have an 07 sportster 1200. It was my dads, he has never been very good about maintenance on it. I've done some research and have seen that Harleys like the vr1 20w50. Which would be the better option in that, the conventional or synthetic version? Also he had an oil change down just after winter andI just found out the oil used was bel ray non synthetic. The motor seems to currently be quite noisy in the valve train. What oils would you recommend?