Okay, I missed the stainless steel language on the letter for my 4014 (I was too excited about the production numbers, I guess
), but I believe the slide is carbon steel. I have many, many letters from Roy regarding 3rd generation autos. You should note that Roy has "stock language" that he inserts into each letter discussing a "series" generally. In fact, in his letter regarding my 4676, he has a fair amount of language about the 4526, including production figures (1,365 units of the 4526 and 1,386 units of the 4576).
I checked the factory letter on my 4013, which does have a stainless slide, and the language of that paragraph is the same. I think he just stuck in some "stock" language from his 4013 letters. Keep in mind that I'm sure he's done way more 4013 letters that 4014 letters.
If you read a number of Roy's letter you will see what I'm talking about.
FWIW