70herald, STP is definately more than an oil thickner. There is a definite attraction to the metal [& your hands etc] which stops the oil draining off.
I was using it in a Hewland transaxle [crash box] in a Lotus 20 F2 open wheeler. During a rebuild we discovered that one tooth of the crownwheel had a crack at its base.
While we were waiting for a new crownwheel, & pinion to come from UK, I did one race with it, with STP in the oil. After fitting the new gear, the old stuff was thrown in the long grass, out the back of the shed.
Nine months later a mate with the same box asked me if I had a spare of that ratio, which he could not get in time for a race. I told him about my old one, out in the grass, which I thought would be rusted half away. He thought it was worth a look, & came over.
After 20 minutes ripping the grass out, we found them, half burried in the dirt.
That crownwheel & pinion were perfect. There was not one trace of rust, they were still slightly sticky with oil, & had that STP smell.
As the STP patents have now expired, I believe that some of the newer products are using the same technology.
Phil