Find text inside a Word document Text Box from VB

Help please;
I am building a Visual Basic 6 application that prints vouchers from MS Word 2000.
I have built a word template document that looks like the voucher, with marker text in the places of details that will change from voucher to voucher, such as amount and expiry date. my intention is to open this word document from vb, find and replace the amount and expiry tags with the required text, print the document and discard the changes.
This works fine except for one thing. the expiry tag is in a Text Box on the word document (to anchor its position) and the vb code I am using fails to find it.
How do I find text inside a Word document Text Box from VB?
TIA

   Dim appWord As Word.Application
   Dim oDoc As Word.Document
   Const wdReadOnly = True
   Const wdNoSave = False

   Set appWord = New Word.Application
   Set oDoc = appWord.ActiveDocument
   appWord.Documents.Open "C:\VoucherTemplate.Doc", , wdReadOnly

   'Amount
   With appWord.Selection.Find
      .Text = "%AMNT%"
      .Replacement.Text = lblValue.Caption
      .Execute Replace:=wdReplaceOne, Forward:=True, _
         Wrap:=wdFindContinue
   End With
   
   'Expiry Date
   With appWord.Selection.Find
      .Text = "%EXPIRY%"
      .Replacement.Text = lblExpiry.Caption
      .Execute Replace:=wdReplaceOne, Forward:=True, _
         Wrap:=wdFindContinue
   End With
   
   'Print out the result
   oDoc.PrintOut
   
   'Clean up
   oDoc.Close wdNoSave
   Set oDoc = Nothing
   Set appWord = Nothing