Hammers on Lifter gun not set right

[Taylor Heiner]

So I have an 1876 lifter gun that I I took apart because the left hammer was not at the correct position, it was always resting against the firing pin rather than having a bit of clearance, causing the firing pin to stick out a little at the breech. After I took it apart I saw there was a little bit of wear on the resting pin and mainspring so I tried to shim it but that didn’t fix the problem (it is not as thick as it appears in the photos and I will probably be removing it soon). I checked all the parts and I don’t see any bent parts compared to the right side which is fine. The only thing I can think of is that the hammer shaft must have spun in the press-fit. Has anyone run into this before? If it is the press fit, is there any way I can make it so it doesn’t slip again without welding it? This is a low-grade gun and I really don’t want to be dumping lots of money into it on complicated repairs.