These engines (OM60x) are famous for lifter noise. Thankfully, my car has never had a problem, but I know of many who have. The bottom line is, the only thing I know of that helps is switching to synthetic oil. I know of more than a few individuals that claim immediate benefits in lifter noise reduction following a switch to synthetic. A few folks, as yourself, reasonably determined that the lifters needed to be replaced, only to have the problem return shortly thereafter.
'04 ML500 - 53k, Inspiration Edition, Desert Silver
'11 Audi A4 Avant - Brilliant Black
'87 300SDL sold
'99 C280 Sport sold
'85 190E 2.3 sold