[ecfisa]

Hola bigguntm.

Proba de este modo:

Código Delphi [-]
...
procedure TForm1.FormCreate(Sender: TObject);
begin
  with MaskEdit1 do
  begin
    EditMask  := 'LLL-00000-000;0; ';
    CharCase  := ecUpperCase;
    Text      := '';
    MaxLength := 12;
  end;
end;

procedure TForm1.MaskEdit1KeyPress(Sender: TObject; var Key: Char);
begin
  with MaskEdit1 do 
    btnCalculate.Enabled:= SelStart = 12;
end;
...

Saludos.