You mention a nailing problem, bad enough you want to shoot it. I recall working through some strange noises last year on mine. They turned out to be some real bad valve springs. However one of the bits I picked up from a very experienced MB tech, was that the prechambers will on occasion get loose in the head and make a racket that sound a lot like nailing.
Since you are having troubles there I thought I might add to the mix here a little. BTW the tech said the best way to check that is just to torque them to specs. And that requires a special tool.
Just can't win I guess...