I used Redex Petrol Injector Cleaner (green label) for many years (not on the Merc), and I personally think it is a great product.
But many believe that Forte is better than Redex.
I am not using any fuel cleaner additive on the Merc, because MB say that fuel additives are not permitted so I tend to follow their advice even if the car is no longer under warranty. MB say that use of additive is only permitted when they have been added to the fuel at manufacture i.e. not added to the car's petrol tank by the car owner / driver.
What I do is use Shell V-Power instead. V-Power has detergents added to it, and regular use keeps the engine clean.
If regular use of Shell V-Power is too expensive, you could put some Shell V-Power or BP Ultimate in the car when the tank is empty, drive it hard for a while (i.e. revving the engine), and repeat this every few tankfuls.
For a diesel, would you recommend using the Redex on the W221? I guess it works out the same if I fill up with V-Power and test that, or regular diesel and add the Redex.
