I'll be speaking to Jerry to put this thing to bed, and as a Trustee at our Museum I will check when I am next in, but don't think that sort of point would be recorded!!
Addition: I have just checked through the L42 lists of rifles, and the only one earmarked as a potential right off during the Falklands War, is the one I hold which was rebuilt. There are no other entries to say that a rifle was lost, but a couple that were damaged a few years earlier than the war of 82.
Donnington was clearly the disposal location, but there is no mention of Royal Marines at all on the lists, so I have to assume (probably wrongly) that they have their own as mentioned earlier.
Simon might like to corroberate that.