My PM9 had the infamous "barrel peening" issue when I bought it. I talked to Dottie at Kahr, she asked me to send it in. I asked if I could just send the "top half", thereby removing the need for an FFL or FEDEX. No problem.
I sent in the complete slide, barrrel and recoil spring assembly. Kahr replaced all of them. It has worked perfectly ever since, with any ammo I can fit in the mag.
I carried it for three years until I upgraded to it's bigger brother, the P45, which I am carrying now. I still have the PM9, though--it's not going anywhere. It is (for me) the perfect pocket carry pistol. I am 5"9 and 150 lbs.
My PM9 has a "VA" prefix. IIRC, those were the ones with the barrel peening issues. If I were looking at a used PM9, I would try to test fire it first, preferably with your intended cary ammo. If it is a VA serial and the previous owner contacted Kahr, there is a good chance the "top half" has already been changed out. Perhaps Kahr could even tell you if you call them with the s/n.