I suspect my 2004 C320 4matic sedan with an M112 engine has a bad rocker arm. I will verify the problem shortly. I see that Pelican Parts sells the arm. Does it come with the hydraulic lifter as pictured, or does that need to be ordered separately? Also, I understand that the arms are pressed on the rocker shaft. Do I need special tools to change one rocker arm? Are there any instructions available online?