We've got one or several real noisy lifters (or what ever there called by MB) in our 3.5L 2003. It has 86,000 miles & has had regular oil changes within the proper miles (with Mobil 1 0-40) however apparently this was not enough with the short trips that my wife uses it. Next time around I will be changing about every 4500 miles IMO. Anyway, the dealer dumped the oil & added a qt of ATF to try & clean it, then I changed this after a week of running & used Mobil 1 0-30 with a qt. of Rislone. None of this has done any good yet. I don't think it will. They say that these arn't conventional hyd lifters like I am use to in an old V-8?, you don't change them all, is this right? Should we just change out the bad 1 or 2 on the pass. bank & forget about the others till they go bad? Or should we do them all? I don't know the cost difference yet but oviously it would be cheaper to change 1 or 2 on the same bank rather than doing them all. There still checking with the tech. & haven't advised me yet. What's the opionions out there?. At this point were a little "tight" & would rather not do them all if we can get away with it. Thanks