I've used B-12 at times, and I don't find it to be any better or worse than any similar product. Your guy has probably had good results with it, so he promotes it now. Additives fall into two basic categories, solvents and lubricants, or some mixture of the two properties. The fuel stabilizers are somewhat different, having some sort of varnish inhibitor that's supposed to keep stored fuel from going stale. I've always felt the best way to put an engine's fuel system into moderately long storage is to empty as much gas from the tank as possible, run the engine to purge as much remaining fuel as possible, and use some type of fogging oil to prevent rust and ring sticking. Blocking off the intake and exhaust system to prevent humidity from promoting rust as temperature changes migrate air in and out of cylinders with open valves is probably the best thing to do for a stored engine.
Jerry
