The pistons are not chrome plated. That would be prohibitively expensive. Those talking about cerakote, that would not add any corrosion or abrasion resistance.

The titanium nitride (or copper nitride for that matter) usually needs to be plated on a material that will accept it such at nitralloy 135 (that material is used on fighter jets). You cannot machine nitralloy or nitride coatings easily so you would have to pay a grinding shop to hit the final OD of the piston ($$$).

So at the end of the day you're better off buying a new set of OEM calipers and change your brake fluid every year if you're worried about corrosion,

You can also pull off the dust boots on each piston and regrease them periodically. You're trying to reinvent the wheel where it's not necessarily warranted.

-aerospace engineer

Has anyone noticed a lesser amount of seizing based on which fluid they use?

I'm about to change my rotors and pads out and I'm going to full fluid flush as well. I used to use ATE Super Blue back in my racing days which now seems to be the ATE Type 200 Amber fluid now, thinking about that as it has good water binding properties.

Anyone use the stuff in our 4th gens?

The OE pistons are not just polished steel, they are chrome plated. They have excellent corrosion resistance. The issue is that moisture collects around where the boot fits to the casting...then slowly creeps under the boot and around into the bore where as the paint or zinc plating degrades, pinching the piston...as seen in your picture.

The problem becomes worse in rebuilt caliper because the surface where the boot fits is no longer a clean machined surface, but a blasted more porous surface...so the boot doesn't seal as well as it once did.

Once the caliper is all cleaned up and re-assembled, pull the boot back and squirt it full of silicone dielectric grease...then burp the air out until grease oozes out of it. Once it's full of grease, it won't get able to get full of anything else and it will live considerably longer.

This is not a toyota specific problem.