If its running good and not using oil then leave it alone! Actually the only product I would use would be Valvoline synpower oil treatment, its loaded with Moly and ZDDP. It will also thicken the oil a little. Or just use a High millage oil, they tend to have more additives.
I have used Restore before and had good results but I wouldn't put in an engine that is running good. A lot of people will call it snake oil but most of the reports of people who have actually used it say it helps reduce smoking and increases compression.
It seems like ZMAX had a bunch of lawsuits, one form the FTC stating it was only mineral oil. I have never used cermax. This is from the cermax website...
EMISSION TYPE W/O CerMax WITH CerMax
(6 miles later) WITH CerMax
(458 miles later) EMISSION REDUCTION
Hydrocarbons 68ppm 3ppm 2ppm 97.05%
Carbon Monoxide 0.54% 0.04% 0.03% 94.44%
Nitrogen Oxide 377ppm 107ppm 22ppm 94.16%
Can anyone spot the BS ??