“ ......but I wonder if it is simply a part that wasn’t yet phosphated?”
Interesting, but I don’t know how the phosphating process works. I know I’ve seen several examples of these late ac PP’s with the fire blue extractor just like yours. I thought a particular part would be bare metal and the put into a “phosphating tank”, but that was just my uneducated thinking.
The late ac PP’s all have standard things going about them. As they get later in serial number, things start getting weirder. The really neat ones are the slide stamped serial numbered ones where there is no frame serial number. Some super late ones are in the white with mixed blued and phosphate small parts with wood grips. It starts getting crazy as the serial numbers increase. I had a late ac PP mismatched pistol where the hammer drop wouldn’t work. I had another super late ac PP, in the white, where the ejector button wouldn’t allow the mag to be inserted. I had to push in on the ejector button and push up on the mag to get it in the gun. It would eject the mag just fine though. I found that the metal in the frame wasn’t drilled fully to allow the mag ejector switch to be fully seated, causing the button to be an obstruction. It would lock the mag in okay though and eject the mag just fine. But getting it into the gun there was the extra step that had to be done.
There’s actually a data base with these that have been kept and added to. Yours is not on it, so it hasn’t been reported. Check it out:
http://p38forum.com/forums/attachment.php?attachmentid=80059&d=1532025164
Also, good threads on these:
http://p38forum.com/forums/showthread.php?t=29314
Wood grip ones are neat too. I had a late PP ac mismatch that I bought pretty cheap with a set of wood grips. I turned around and sold it to get something else. I found the wood grips to be a really “thick grip” when holding the pistol. I was so used to the thin plastic type that I didn’t realize how thick they really felt until I got that pistol. Watch out on the wood grip type as some have had varnish applied to them. They should be that dried light color wood. Of course some are dirtier with age, but you’ll know what to look for and what you are seeing when you come up on one.
On your mag base; yes, that crack adds to the idea that it was a rejected part found and added to your mag.
A lot of people look at these cracked parts, parts that don’t work, etc. as a bad thing and don’t want them. Serious collectors that study these know what they are; not crap but actually what was going on and you are holding it. No telling how many real “messed up” guns have been ruined switching things around. Luckily you got ahold of that mag because it probably would have gotten switched aound with the “proper” mag floorplate.