Заменить в строке все предыдущие вхождения последней буквы заданного слова на точку

Function Transf(ByVal S As String) As String
   ii% = 2
   Do
       If (Mid$(S, ii%, 1) = " " And Mid$(S, ii% - 1, 1) <> " ") Or _
          (Mid$(S, ii%, 1) <> " " And ii% = Len(S)) Then
          If ii% = Len(S) Then
             last$ = Mid$(S, ii%, 1)
             jj% = ii% - 1
          Else
             last$ = Mid$(S, ii% - 1, 1)
             jj% = ii% - 2
          End If
          Do
             If (jj% < 1) Then Exit Do
             If Mid$(S, jj%, 1) = " " Then Exit Do
             If Mid$(S, jj%, 1) = last$ Then Mid$(S, jj%, 1) = "."
             jj% = jj% - 1
          Loop
       End If
       ii% = ii% + 1
       If ii% > Len(S) Then Exit Do
   Loop
   Transf = S
End Function

Function f$(s$)
  Dim x, i%
  x = Split(s)
  For i = 0 To UBound(x)
    If Len(x(i)) Then x(i) = Replace(Left(x(i), Len(x(i)) - 1), Right(x(i), 1), ".") & Right(x(i), 1)
  Next
  f = Join(x)
End Function

Function f$(s$)
  Dim x, i%
  x = Split(s)
  For i = 0 To UBound(x)
    If instrrev(x(i),Right(x(i), 1),Len(x(i)) - 1) Then x(i) = Replace(Left(x(i), Len(x(i)) - 1), Right(x(i), 1), ".") & Right(x(i), 1)
  Next
  f = Join(x)
End Function

Function f$(s$)
Dim x, i%
x = Split(s)
For i = 0 To UBound(x)
    x(i) = Replace(x(i), Right(x(i), 1), ".", , Len(x(i)) - Len(Replace(x(i), Right(x(i), 1), "")) - 1)
Next
f = Join(x)
End Function

Function f$(s$)
Dim x, i%
x = Split(s)
For i = 0 To UBound(x)
  if Len(x(i))>1 then
    Do While InStrRev(x(i), Right(x(i), 1), Len(x(i)) - 1)
        Mid(x(i), InStr(x(i), Right(x(i), 1)), 1) = "."
    Loop
  end if
Next
f = Join(x)
End Function

Function f$(s$)
  Dim x, i%
  x = Split(s)
  For i = 0 To UBound(x)
    If Len(x(i))>1 then if instrrev(x(i),Right(x(i), 1),Len(x(i)) - 1) Then x(i) = Replace(Left(x(i), Len(x(i)) - 1), Right(x(i), 1), ".") & Right(x(i), 1)
  Next
  f = Join(x)
End Function

sub aa()
msgbox f("МОЙ ТЕКСТ")
end sub