Deleting Duplicates of Second Instance

My previous procedure only searched columns A and B. I didn't realize you wanted to check C against itself. The procedure below should achieve that. I believe it will also remove the "1" at the start of any number in column C. Let me know if it works...

Sub ClearDupesInC()
Dim LastC As Long
Dim LastB As Long
Dim i As Long
Dim j As Long


Application.ScreenUpdating = False
LastC = ActiveSheet.Cells(Rows.Count, 3).End(xlUp).Row
LastB = ActiveSheet.UsedRange.Rows.Count

For i = LastC To 2 Step -1       'if you have no header, go from LastC to 1
    If Left(Cells(i, 3).Value, 1) = 1 Then
        Cells(i, 3).Value = Right(Cells(i, 3).Value, Len(Cells(i, 3).Value) - 1)
    End If
    If Cells(i, 3).Value <> "" And Application.WorksheetFunction.CountIf(Range("C2:C" & LastC), Cells(i, 3).Value) > 1 Then
        Cells(i, 3).ClearContents
    End If
    If Cells(i, 3).Value <> "" Then
    For j = LastB To 2 Step -1   'if you have no header, go from LastB to 1
        If (Right(Cells(i, 3).Value, 8) = Right(Cells(j, 2).Value, 8) And InStr(2, Left(Cells(j, 2).Value, 4), Left(Cells(i, 3).Value, 3))) _
        Or (Right(Cells(i, 3).Value, 8) = Right(Cells(j, 1).Value, 8) And InStr(2, Left(Cells(j, 1).Value, 4), Left(Cells(i, 3).Value, 3))) Then
            Cells(i, 3).ClearContents
        End If
    Next j
    End If
Next i

Application.ScreenUpdating = True
End Sub