Wow Roger, boy am I glad all that zmax is out of the system in my car.
I think the best thing you can do for your car, based on my experience with additives, is don't bother wit them.
Change your oil regularily with filter, change the tranny fluid regularily with filter, and change the fuel filter and run a bottle of techron through it once every so often.
I just put a bottle of techron in my car, ran it through, changed the oil, and filter, and my car is running great.
Of course I was suffering from tainted gas the last couple of weeks, but finally found a station that had the good stuff. none of the downmixed gas that they are using to help take away our hard earned money.
Be careful out there, some gas stations are switching the gas on you, I know, I have two that will never see my car filling up at their tanks ever again.