I'll throw my 2 cents in and relate a problem and solution that somewhat mirrors yours.
I bought a M9A1. When I got it the trigger was "pretty Good". I followed the tutorial on this forum that deals with the trigger spring and part #45 the weight or as you refer to it as the washer on the spring shaft that rides with the firing pin. I wanted to get the trigger to release the same every time I pulled it. The trigger would most of the time be nice, light, and break clean, other times it would be heavy and gritty. I polished the parts in the tuitorial. The spring(inside) and the inside of part #45, I polished by wraping a piece of 1500 grit sandpaper around a small finish nail. I then put the nail and an edge of the sandpaper in a electric drill, then ran the sandpaper inside the parts to polish. I inserted the guide rod into the drill chuck and polished with 600 then 1500 grit sandpaper.
I LIGHTLY lubed the assembly and re-assembled. The trigger was GREAT,except that after awhile it got REAL gritty and stiff, then would go back to being GREAT for awhile.
I thought about what might be happening and decided that the part # 45 was too big after the polish and was not riding the bar straight, but occasionaly twisting. I also called Steyr to find out what direction the bevel on part #45 faced. They told me the bevel faced TOWARD the spring. They also offered to replace the entire sub frame with trigger assembly on an exchange, VERY GENERIOUS of them. Instead I asked if they would send me a new part #45, they did, I got it in 3 days.
In the meantime I took a large pair of channel lock pliers and squezzed the part #45 as tight to the bar as I could. THAT DID IT! the part #45glides along the bar tight with no slop, but still runs smooth.
GREAT TRIGGER every pull!