Added thoughts
If you visit other sites and ask around you will read stories of cracked frames and slides. It does happen, it happened to me. But it's almost always associated with the use of plus powered ammo or a gun that has been shot a lot. In the case of my gun I can tell from the marking that it was in service at least 15 years as an issued police side arm. While I never used plus powered ammo, I suspect the previous owner did, hence why he put it up for sale. The P-1, based on the German WWII P-38 sidearm, was a German army and police issue pistol. The design was in service for about 40 years so that should provide some reassurance for concerns about reliability.
If you get the P-1, know that only the front sight is adjustable for windage. The front blades are available in different heights (numbered 1-4) for up and down adjustment (or if you have a tall sight, then you do what I did, gring it down a little, test fire, and grind some more a little at a time until you get it dead on).
The rear notch can not be adjusted. Trying to strong arm adjust it will damage your gun.
Unless you have a very good reason, don't try to take apart the slide. It really isn't necessary for cleaning. (Spray in some gun blaster or some such with one of thos tiny tubes thru the firing pin hole, dry it out w/ compressed air, and use a drop of Remoil. The reason is the slide cover can be a b!tch to get on right, and if you don't, subsequent firing of the gun will send the slide cover and a bunch of tiny parts flying all over, some to parts unknown.
Some people recommend replacing all the springs, especially the recoil springs and magazine springs. I did but I wouldn't bother doing it again unless the gun has problems ejecting or feeding and only after I checked all the other possibilities. The P-1 can be ammo picky and simple mistakes can happen. Example, there are 4 ways to put the spring in the magazine, 3 of them are wrong.