fuel additives

[Hocky]

I am still wondering if there are any fuel additives on the market to temporarily increase the power of cars like octane boosters or other power boosters which are safe to be used in Mercedes cars. Mine is a C180 Euro version Classic 1997, with 5 speed automatic trans. I have sent cars for service and noticed boosters added to the fuel tank perhaps to give the owner a false sense of power from the car for a short period to prove they have done a good job. Will these harm the engine? I have also seen additives for "older engines" which adds a fine layer of lubricating matter on the metal surfaces to reduce wear and improve lubrication. Is this all a big deal?