The original macro worked, but not 100% reliably. The following should do the job and you can call it from your main macro before the message box at the end.
Code:
Sub NumberSection()
Dim orng As Range
Set orng = ActiveDocument.Range
With orng.Find
Do While .Execute(FindText:="Assessment:")
With orng
.End = ActiveDocument.Range.End
.End = .Start + InStr(orng, "Diagnosis:") - 2
.MoveStart wdParagraph
.ListFormat.ApplyListTemplateWithLevel _
ListTemplate:=ListGalleries(wdNumberGallery).ListTemplates(1)
.ParagraphFormat.LeftIndent = CentimetersToPoints(0)
.ParagraphFormat.FirstLineIndent = CentimetersToPoints(0)
.ParagraphFormat.TabStops.Add _
Position:=CentimetersToPoints(0.5), _
Alignment:=wdAlignTabLeft, _
Leader:=wdTabLeaderSpaces
End With
Exit Do
Loop
End With
lbl_Exit:
Set orng = Nothing
Exit Sub
End Sub