I have a 2004 E270cdi. It developed a ticking noise in the engine (top part). I took it to a repair shop and they indicated that it is injectors. I then took it to the injector guy. After lots of money, all 5 injectors were either replaced or revamped. They all tested within the range limit set out by MB. The ticking noise continued. The injector guy traced the noise to no 3 piston (by removing the power plug of the injector). He swapped no 3 and 4 injectors.The noise stayed at no 3 piston. I took it back to the mechanic and he opened it up. He says there is nothing wrong with the lifters. All are in perfect condition. The engine guy still insists it is an injector. It is now 4 months that they cannot fix the problem. Please assist.