I paid 450 some years back for a numbers matching 1944 Experimental "E-Series". They have gone up dramatically compared to other C&R Weapons i've followed and collected.
After the war, the P1 was produced. Aluminum frame, and was a hunk of junk compared to the durability of the P38. That being said there are plenty of part kits for the P1 available, cabellas, midway, cheaperthandirt, all have had them from time to time.
For a hundred bucks you get another slide, and all new springs. Few other parts also.. You need to replace those springs if you plan on shooting it. People who don't learn how much a cracked slide is worth.
By your date code I believe that's a mauser produced one. A byf42 is quite rare, 700 of those produced. Mauser production. Should see some other codes, one on side of frame, and one under barrel. The one on the magazine *won't* match the others. This is normal for wartime production.
May see something like WaA over a number 135 for example. That should be same under barrel as the side of the frame. Need three matches excluding magazine for numbers matching. Usually you'll find hand electro-stenciled numbers on barrel from a certain importer. It should match their import required serial number they assigned, and had to stamp onto the weapon.
Look for a Square with an X inside, this is from the russians. Means they reblued it, and replaced anything faulty usually in the Ukraine post 1945. You'll probably find that several times. It's on most Russian made war time weapons.
Being a Russian Capture, doesn't mean it isn't still valuable, just not as much. These are usually the ones you find mass distributed from places like Caballa's midway etc.
Look real hard for that Russian Proof Mark. It may not be a bring back, so original blue would still be there, but you never know, there are a lot of a one of a kind unique items that to certain collectors, means a lot more than to most.
Winchester. Whitebox. 115grain, FMJ. Change the springs and take her to the range. Sounds like an interesting piece based on your date/manufacturing codes. Good luck on a matching holster