The primitive form ᴱ✶mḷgo appeared in Early Noldorin word lists of the 1920s serving as the basis for various “oil” words (PE13/139). It may have replaced ᴱ√ILI “shine oily” from the Qenya Lexicon of the 1910s (QL/42), and may in turn have been replaced by √LIP “oil” from a list of roots from 1968 (VT44/15), though in this list √LIP had no derivatives.
Neo-Eldarin: For purposes of Neo-Eldarin, I think it is worth positing a Neo-Eldarin root √MILIG to salvage derivatives of 1920s ᴱ✶mḷgo.
An unglossed root in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. mile “seed” and ᴱQ. milnar(wa) “sown field” (QL/61). The root ᴱ√mil was also given as the basis for G. mail “flour” in the contemporaneous Gnomish Lexicon, though this Gnomish word was marked with a “?” (GL/56). There are no signs of this root having similar meanings in Tolkien’s later writing.