Out today for some training work with my L9A1. It's a May 2013 model with rollpin and loaded chamber indicator. I've put about 150 rounds through it before today. After about four magazines, I encountered a malfunction where the trigger would not function. Action fully in battery. Round chambered. At home, suspecting dirt somewhere, when I dismantled the upper assembly, including removing the backplate (42) a circlip was noticed sitting free. I suspect that it is the item shown on the exploded diagram as (37). Could not see any way to re-locate it - and believe me, I tried. Anybody know how that could be done - whether the absence will affect anything but operation of the loaded chamber indicator. Is it possible that this item could affect the trigger function ? Having given everything a good clean, I will be checking the gun out again tomorrow.