I am looking for some advice and / or discussion about the different oil manufactures and recommendation Pro's / Con's. The site has quit a few discussion about oil's viscosity with little about the pros and cons of manufactures. My interest is manufactures and how they compare to the recommended Shell Helix. For example adding additional additives like additional Zinc. When I converted to Castrol Edge or Mobil 1 synthetic oil in my old muscle cars I have to add a Zinc additive to protect the cam and hydraulic lifters. This is because the manufactures removed the Zinc! I am not concerned about the viscosity any good oil is available in the proper viscosity. No one locally carriers Shell Helix. Thinking of using Mobil 1 or Castrol Edge.