As 2152hq made mention of, the slide of my surplus P-38 ( or was it a P-1, can't remember for sure ) also cracked at the locking bolt cuts. The gun appeared to be in nice condition, but obviously I have no idea of the overall round count. Now I have used, and continue to use, quite a bit of NATO, +P and +P+ ammo, but NOT in the P-38/P-1. Mine cracked after just a few magazines of commercial standard pressure ammo. I knew the post war P-4 had a beefed up slide, but just very recently learned there was such a thing as a beefed up "fat slide" for the P-1 version. Given my, and apparently other's, experience with the P-38 slide's cracking, I would not personally be interested in buying another P-38 type pistol to shoot, without the beefed up slide.
btw, I had always heard that Lugers required rather warm ammo. The one I acquired within the past year, 1938 Mauser version, functioned most reliably with the lightest factory load I have chronographed in over 30 years. That most reliable load in my Luger was the Federal "red box" American Eagle 124 grain round nose at just over 1000 fps. I would have bet against that...