STP? I don’t think so. STP oil additive actually thickens your oil and it does not contain any detergents, so if anything, this goo might make the situation worse, rather than better.
I would suggest that you add 1/2 a can of Seafoam to the oil, and then change the oil within a day or two. Seafoam will frequently free-up a sticky lifter, and for far less money than tearing down the engine. Just be sure to change the oil within 100-200 miles after you add the Seafoam to the oil.
And, in the future, I would suggest that you schedule your oil changes more frequently, in order to avoid a recurrence of the problem.