Rear element reassembled. Putting the rear retaining ring back was a bit of a joy...After that kind of damage, it will never go back on like new. I lubed it up a bit with some grease and used the scribe to carefully put it back in. It took a little bit of cohesion and some light tapping with a rawhide mallet to prevent cross threading but it went back together eventually. I put some black electrical tape over the entire thing to keep dust out because there was some minor air gaps between the retention ring and the barrel due to the deformation.