An ex-Marine writes here about the difficulties in properly cleaning/maintaining weapons. I wasn't a Marine, but the piece seems valid to me.
It struck a chord because I remember the captured soldier in the early days of the Iraq war. For a while she was made an icon of the fighting woman. Eventually it turned out that her weapon jammed so she never fought. I had sympathy for her. I don't think I ever cleaned my weapon in Vietnam. As a matter of fact, there was a screwup in getting my departure orders to me, so it was a mad dash to get to Camp LBJ and go through out-processing, one step of which was turning in my weapon. When I tried to, the guy (spec-4 maybe?) refused to take it until I cleaned it. I tried to explain the situation, my flight was due out shortly, but he was adamant. Finally I threw some money at him >$50<$100 and he agreed to take it.
I made my flight.
(It seems possible that the Russian soldiers fighting in the Ukraine have been as lax in their maintenance as I was. )