Not necessarily true. This is a pretty common problem due as mentioned, to the less than stellar design of the threading surface. You have to judge how bad it is to decide on the right or best course of action. The best solution and the only thing to do if they have actually failed in service is to replace the arm. You can weld (not tack) one back in, but then you got a boogered up POS. If they just don't torque down right on replacement, tacking them in is a viable option.
