You need to do a compression test to see if you can figure out which set of rings have the issue. The compression rings or oil control ring. Worn valve stem seals show up as oil burning at startup after sitting for several hours.
A fuel additive may help with compression rings. And an oil additive with the oil control rings.
Cold engine yes but idling and off throttle braking can result in increased manifold pressure which can draw oil past worn valve stem seals.
You could compression test the cylinders but you know it's not gonna have great compression since it's consuming oil. Unless you're willing to plunk down the cash, in the event of really bad readings, to replace the rings, I'm not sure the ROI is favorable on a compression test.Symptoms of bad valve stem seals
If the rings are worn, this oil won't help. If they are stuck or dirty, it will.