Far as I have been able to find out STP oil Treatment was a thick oil with ZDDP added to it with maybe a few other additives. If you have a car or truck that burns oil it might be better just using a thicker oil (in the summertime) like 20W-50. Or try a Auto-RX cleaning and see what happens.
STP did come out with an oil extender that according to what I heard was supposed to be a good product. But apparently it did not sell because as far as I know they took it off the market.
Thick oil like a 15W-40 or a 20W-50 will slow oil burning and oil leakage.