Question about servicing, changing springs, slide return, and rail damage!

[Kahr9]

Hello,

I am new here, own 2 Kahrs and I am buying a third (MK9). Currently own the PM9 and the K9. I have bought all of them used.
The K9 has given me ZERO problems regardless of ammo or conditions.

I have a few random questions:
1) The PM9 has been pretty solid for a small polymer pistol but the slide often does not stay locked back after the last shot... anyone else experienced that? What did you do to fix it?
2) The PM9 is newer, but the K9 and the MK9 are a little older, the K9 I think may even be from the 90s. Like I said I bought them used... should I replace the springs on them? What are the recommendations for servicing Kahrs and what springs should be replaced? I have seen the spring kit on Kahrs website which includes the: trigger bar spring, slide stop spring, slide stop spring screw, magazine catch spring, recoil assembly, striker spring, striker block spring, and extractor spring.
3) I am buying an MK9 Elite03 and I am going to order wood grips for it... should I also order the stainless steel guide rod at the same time? Do they all have plastic guide rods and do the plastic rods ever fail? The spring kit for the MK9 says it comes with the "recoil assembly" so I am assuming this includes another plastic guide rod, it's a shame they don't offer it with the SS rod.
4) The internal frame of my PM9 has been damaged (and it has low round count) in the area immediately to the right (when standing behind the gun) of the feed ramp (approximately the area that the ejector sits against when the breech is closed). Has anyone noticed this area getting chewed up? I figured it was from the slide slamming back down without the resistance of another round to reduce its momentum (I do a lot of dry fires).

Thanks! I have used this forum many times but have never joined!