I believe there's a way to do it much simpler. But you'll need to test.

DECLARE @StartDate DATETIME

DECLARE @EndDate DATETIME

SET @StartDate = '1/1/2012'

SET @EndDate = '1/31/2012'

SELECT ER.EngEquipID

,ER.Location

,ER.Cycles

,ER.DateTimeStamp

,'Labor' AS Labor

,ISNULL( A.TRANS_tambase_amt, 0) AS LaborAmount

,'Parts' AS Parts

,ISNULL( B.TRANS_tambase_amt, 0) AS PartsAmount

,ISNULL( A.TRANS_tambase_amt, 0) + ISNULL( B.TRANS_tambase_amt, 0) AS TotalAmount

FROM Engine_Prod.mc.WORKORDER WO

LEFT OUTER JOIN MSM.dbo.tblEngRunData ER ON ER.WONumber = ltrim(rtrim(WO.id))

LEFT OUTER JOIN mc.WORKTASK WT ON WO.wordoi = WT.wrkord_oi

LEFT OUTER JOIN mc.WORKORDERTYPE WOT ON WO.wot_oi = WOT.wotyoi

LEFT OUTER JOIN (

SELECT CHARGEINF.wt_oi

,LABORTRANS.tambase_amt TRANS_tambase_amt

FROM mc.CHARGEINF CHARGEINF

INNER JOIN mc.lbtr_chgs lbtr_chgs ON CHARGEINF.chgioi = lbtr_chgs.ref_oi

INNER JOIN mc.LABORTRANS LABORTRANS ON lbtr_chgs.owner_oi = LABORTRANS.lbtroi

WHERE LABORTRANS.posted = 1) A ON WT.wtskoi = A.wt_oi

LEFT OUTER JOIN (

SELECT CHARGEINF.wt_oi

,INVTRANS.tambase_amt TRANS_tambase_amt

FROM mc.CHARGEINF CHARGEINF

INNER JOIN mc.intr_chgs intr_chgs ON CHARGEINF.chgioi = intr_chgs.ref_oi

INNER JOIN mc.INVTRANS INVTRANS ON intr_chgs.owner_oi = INVTRANS.introi

WHERE INVTRANS.posted = 1

) B ON WT.wtskoi = B.wt_oi

WHERE ER.DateTimeStamp BETWEEN @StartDate

AND @EndDate

AND WO.clsdt_date BETWEEN @StartDate

AND @EndDate

AND WT.ci_cnc_date IS NULL

AND WT.tmplt = 0