I don't trust the Shell stations in my area. Two are independent, and they have choice locations by being located right off the interstate exit ramps. The other Shell is not an independent, and I use to get just the regular gas there at a premium price. Sheetz just moved in town, and opened two locations, and my Oldsmobile idles smoother on the Sheetz gas for what ever reason, and it's cheapest gas in town. There is one Mobil station in town, and I do like their gas, but they charge a .20 cent premium at least over other stations, and I have to go out of my way to get it.
Enough of my rambling. I would buy the Techron additive because at least you know you are getting what you paid for.