Grills have been removed and repair is almost ready. It needs some filler, sanding and a new paint at the end.
Defect was replaced by glass fiber kit (green). To give the form a stock was made of a piece of aluminium plate covered by foil tape to make removal easier. Then it was strengthened by a layer of glass fiber and two layers of epoxy resin on both side. It looks quite good...
Hopefully it will be longlasting.