1997 E420, 163K miles... vehicle has had a ticking hydraulic lifter noise in the right cylinder head for the last 60K miles or so. Oil tubes have been renewed but the noise remains. Vehicle has been using Mobil 1 since new. Should the faulty lifters be replaced? Any harm to the engine if the lifters are not renewed?

How do you know the oil tubes are still good?

I've seen some of the lifters score their seat when left dry from not getting the oiler tubes replaced and driving around for a year or so like that.

Oil tubes were replaced when lifter noise originally appeared. Recent inspection reveals tubes are still intact.

JG, your motor's gonna tick a little bit regardless. All of my 119's tick to varying degrees. Mobil-1 is so thin and efficient it'll make the whole valve train seem louder, but in reality it's just fine.

Another source of ticking are the injectors. It's a different tick, sort of a clack - you'd have to hear it. I had one that drove me out of my mind trying to figure it out, but sure enough it was the injector body.

And finally, a VERY common source of ticking on that motor is from exhaust leaks. Usually right at the header attach points. Often you'll have to pull the headers just to get to the rear O2 sensors, so go ahead and do the gaskets and attach points to the exhaust tubes etc while it's off. It's not quite as cramped on your motor as the 5L. I’ve seen oil tubes replaced on both sides when it was a loose exhaust bolt the whole time. It’s a great “gotta do it just cause” item at most indy’s, along with evaporators.

Like somebody mentioned, lifter faces can "gall" from lack of lubrication, and it usually shows up on the cam lobes also. See the DIY on this website. The guy that wrote it is a PhD with a big 3-letter gov't agency, and a frequent contributor to this site. I know him well.

If you’ve done oil tubes and the difference didn’t knock you over, then you haven’t found it. Keep it up, you’ll find the source before long. But please – don’t get carried away with the totally silent motor concept. As balanced and smooth as 119s are, they will still clack around to some extent. AMG does a pretty good job of making them even quieter too.

Good luck