Mercedes does make a filter for that engine. I priced them a few weeks ago. They are like 28.50 each. Bosch & Mann make filters for them, as well. I am not convinced they are OEM, but possibly just made to Mercedes' specifications. On the lifter noise it should not happen on hydraulic's. However, it can an does happen. Especially, in cooler weather, and with a motor, that has milage build-up. Also, the oil that is in it has a factor to do with it. If it is not in the perscribed range in the manual for the engine, and ambient temperatures. Your oil pressure gauge should jump right up on start-up very quickly. The only other slow rising of the pressure should be after an oil change.