No clue about your leak, but here is a tip on a removal tool: We have 3408 TADI marine engines in our yacht. I think the injectors may be mounted in the same way on the 3406. The thread on the top of the injector is M14x1.5 and we just made a brass pipe with this thread in one end and a M8 thread in the other. Screw it on the injector and put some heavy nut or similar on a long M8 bolt in the other end to use as a sliding hammer. Tap lightly on the side of the pipe while pulling the weight along the bolt. Worked great for me!