I have several of these problems. The backpack issue depends on if the flap on the backpack is secure in the main body or not. Still, the left leg is often left not secure. The plane does droop a bit but I have no problems with the intake covers that my 1/48 Stealth J doesn't have. The intake cover one one of my legs, probably the one with the gap that doesn't connect well with the backpack, is loose and tends to fall out easily.
The posts about people having these switching out nightmares confuse me. I'm new but is there any reports of this happening? I mean you have to be a very shady business to do something like switch out products. Mine was purchased brand new on Amazon and had tape securing the plane to the ghost booster blister. It seems that the Zero line is just a failure on yamato's part.