First off....I seriously doubt that the gun will hve problems. I still have a 1911A1 made in 1942 and although I don't shoot it, it has been to Vietnam and who knows what before that. The gun functions flawlessly.
I can only tell you that when I got mine that had a bent sight, I sent it to Travis at HK Customer Service (which has been truly amazing in my years of experience with them) and asked him to replace all the springs and polish the feed ramp just so I would have peace of mind. It cost very little and the gun is amazing. If you haven't held one, you should learn about the decocking/safety feature of the gun because it is truly unique. If you are going to use the gun for SD or carry purposes, you will have to practice a lot to be sure of yourself in an emergency. That's my only reservation for personal defense with the gun. If I practice more, there will be no problem: same as any pistol. Also, as I mentioned, you will pay anwhere from 60 - 80 dollars for a magazine. Two are plenty. If you need more, you will have to search. They are out there. I found a guy that had five stuck away in his safe. I bought two and felt darned lucky to get them for 65 dollars apiece. Your luck may vary.
One last thing. I have no doubt whatsoever that if you get the gun and don't like it, you can sell it for a profit the next week. Keep it a while and then decide, imo.
Again, check on HKPRo for P9S enthusiasts. Many of those people own several P9S models.
Another discontinued HK that is a must-have in my opinion is the P7. YOu can get a German police trade-in for around 600. Those little 9mm. have an amazing trigger and accuracy as well. NOt a .45, unfortunately, but still a great little pistol. Good Luck!