No issues at all with the arms filling unless I shoot the mold to slow.
Even with the "defective" molds, I can shoot the mold slowly (real slooooow) and then push hard and hold. The arms fill perfect every time and no dent in the body if you wait to de-mold.
Going slow on my molds works and does help with the laminate looking good.
Are you sure your plastic is warm enough? We all have the same molds I believe. I am shooting around 330-340 or so I'd guess. (Never have used a thermometer in my pouring life.)
Jim