NG, The locking lug (small lever at the front left side of frame) appears broken. It's a little hard to see in the photo so I'm not 100% sure. The more I think about it, you are probably correct in getting a Luger specialist to help with dissasemby and analyze your problem. Lugers are pretty quirky and can be damaged (i.e. the locking lug) by improper work. Also I was wondering if this is a numbers matching Luger? Salt Flat