All the additives in the world do one thing, lighten your wallet.
Flushing your worn out engine with a can of snake oil will push it over the edge.
You need to determine the issue by using the info these guys gave you to figure out the EXACT problem. Until then you are throwing money at it blindly.
If you determine the rings are worn and it is blowby (which is almost 100 % gauranteed) you can dump in an oil change and substitute a quart of oil with a can of lucas oil stabilizer . That may help you 'limp " along for a while longer.
Dont expect a miracle though.