I have seen this a few times and admit back when I first started to tinker with Parkers I caused this to happen a couple times. My friend Ron Granger (RIP) explained how to compress and hold the mainspring under tension until the screws were out. The striations on the screw shaft are caused by removing the screw without first compressing and holding main spring tension. Unless this is done, once the screw threads are free the mainspring will push the screw and hold it fast against the frame. You are then stuck with twisting the screw free with pliers and causing those striations. The other surprise if you don’t have the frame wrapped in a shop rag, the mainspring and mainspring plunger come flying out and can be a challenge to find in some obscure nook of your shop floor. Cheers Jack
Hammer screws
Threaded Mode