car info: 2006 w211 E350 japan spec with 77k km  radiator tank had a leak and have splashed small amount of water into the engine bay.. tank got emptied in a week and got check coolant level error message... changed the tank! in a week i got the error message again but this time it was half there cuz only the cap was bad (because it was used)... replaced it with the org problem: I noticed a small tick tick noise when the car was running 2 days ago i didn't really cared. Today all of a sudden