When I was in the German army in the 1970s, conventional wisdom was that the alloy frame and cast steel slide of the P1 was meant to be good for 5000 rounds. Which was plenty because I'd be surprised if any of ours had more than 50 rounds fired through it in a year. During the Cold War, pistol shooting was just not a priority (When the British Amy officially surplused out the Enfield and Webley .38 in the 1960s, ammo allocations were supposedly down to 2 rounds per gun per year
).
I've owned a couple 1960s and 1970s vintage P1's since they started appearing on the surplus market here. None has cracked or come apart on me, but I only shot them moderately for historical interest. If you're looking for a volume 9mm shooter, a Bundeswehr P1 would not be my first choice, though.