If I understand your data correctly, I think the following will work (I essentially just added the sub-query stuff):

SELECT ;
  Equipinv.mfg, Equipinv.model, Equipinv.sernum, Stumaint.clsdate,;
  Stumaint.trhrs, Stumaint.drhrs, Stumaint.udrum, Stumaint.proller,;
  Stumaint.froller, Stumaint.slpring, Stumaint.brushes, Stumaint.ctlhd,;
  Stumaint.audhd;
FROM ;
  eng!equipinv ;
  INNER JOIN eng!stumaint ON Equipinv.cmaster_index = Stumaint.cmaster_index ;
WHERE ;
  stumaint.udrum = .T. AND ;
  stumaint.clsdate = ;
    (SELECT MAX(stutemp.clsdate) ;
      FROM stumaint stutemp ;
      WHERE stutemp.cmaster_index=stumaint.cmaster_index) ;
INTO ;
  CURSOR result

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--Brad