Very,... very,... lucky I´ll say..., I couldn´t find any post talking about this joints in Toynami Valks, but I surprised when I rode in this thread about some reports on cracked shoulders.
The first time I noticed this in my valk, it looked for me like a "special" fine line for avoiding future stress in the plastic, but now, I´m sure, it´s a very bad QC issue, cuz the piece is very small, and the bit on the arm is almost exactly the same size of the hole, so when they assemble it, the plastic fails.
Maybe u got a second row of fixed details on this, like Yamato´s doing with the ZERO line.