My local Autozone has quit carrying 20w50 motor oil that I run in my engine and had it reduced to $2 a quart, so I bought all they had left. I typically run VR1 oil which has some zinc it in, but I bought some reg Valvoline oil and would like a zinc additive to put in with the oil. The car is only street driven, but has a hydraulic flat tappet cam. What additive are you guys using?