Greg,
Sad to say, but I agree with the others. These are classic symptoms of a head/head gasket problem - I know from experience one year ago. Fortunately, my head was perfect and the new updated head gasket solved the problem. Have it checked out by a competent mechanic who knows the OM603.x engine.
Regarding the lifters, though I suspect this is not your issue, I know a guy who has had his replaced by a VERY reputable mechanic THREE times. . . still tapping.
Synthetic oil DOES help. Good luck.