I bought a PM9 in May to use for IPSC Classic division. I have just a shade under 10,000 rounds through it so far and it has been awesome. I added a few things out of the box like you mentioned, magwell, ambi safeties etc but its a great platform for a classic division gun. Zero issues with it so far.
Can I ask what load you are using. I am not having too much luck today so far with 147gr bullets. At 900 fps they are all over at 20 yds. Ha, I ordered the same Magwell.
I shoot campro 147 grain over 3.5grn of n320, very accurate and soft shooting. Chrono around 890fps