If the guarantee fund intends to contest the validity of one of the exceptions mentioned in article R. 421-5, invoked by the insurer, or if it is unable to take a final decision on the matter, it must, within three months of receiving the declaration, notify the insurer and the victim or those entitled on his behalf. It shall also give them its opinion on the admissibility of a claim for compensation from the victim or those entitled on his behalf in the event that the defence raised by the insurer is found to be well founded.