I have used it for a long time when I needed it. I used to add 1/2 quart for a few hundred miles before an oil change at 30K mile intervals or so.

It'* a high quality oil base with extra good additives. I suggest at the end of your current oil change interval that you add 1/2-1 quart as makeup oil if the level is down--or use a siphon tube to drain a quart.

Run it for 3-500 miles then change the oil. Add at least 1/2 quart to the new oil where the additives and the new oil'* additives can work together to clean.

In these days of some high quality synthetic oils suchs as Platinum and Ultra from Pennzoil, I'm not sure the extra additives are needed from Rislone or other additives.

I'd pull each plug wire at the coil and inspect inside. If there'* a lot of brown powder, the wire may be deteriorating and the spark jumping inside the plug wire.

Have you looked under the hood in total darkness to see if you can visually spot the spark jumping? Even a little mist of water from a garden spray bottle on the wires and coils might help make an external jumping spark show up.