Hi - I’m fairly new to the forum and am seeking info as to how/what to use to touchup bluing (?) wear on slide lock lever and other slide control areas. The rest of the slide body is perfect. I was unsuccessful in locating useful content using various search terms in the search function. I am hoping that my learned colleagues within the forum will share their knowledge, and get me started on the right track. In advance, thanks much!

If it is the gun/finish I am thinking it is, it is not Blued but a black finish. You can use a black permanent marker or by some
BC touch up super black

__________________
For office use only

This is what I use for touch-up:

4 oz Oxpho-Blue Cold Bluing : BROWNELLS OXPHO-BLUE(R) | Brownells

__________________
Watch & Pray

I use Van's....it is probably a lot like Brownell's....used on bare steel, works good

If it is this gun, it is not blued.
Slide Finish: Armornite®


ARCHIVE: M&P(R)40 | Smith & Wesson

__________________
For office use only

A better match for today's guns is Brownell's Dicrophan T4.

This is a black not the usual blue color and matches most guns much better.
As as added benefit, it's also possibly the most durable cold blue I ever tried and I've tried almost all of them.

The key to getting a good job is to thoroughly degrease the part with a solvent like Acetone or a soap cleaner, then after drying liberally spray the part or area with 91% or denatured alcohol.
WARM the area with a hair dryer....Note: WARM not hot until the alcohol evaporates and you see light moisture on the part and it disappears.
Apply a coat of T4 wait a few seconds an rinse off with clear water.

Apply alcohol again, warm again and repeat as many times as you want.

Keep in mind the slide, according to Rule3's link, is stainless steel.