That literally makes no sense. A caliper that is going to fail will leak fluid past the seals or past bleeder screws that aren't tightened down. It will be obvious that you have low or lowering pressure. Since calipers are usually installed with new pads and minimum thickness rotors - there isn't going to be a piston blow out and complete loss of fluid/braking power. Even with a leak at 1 corner you will still have some stopping power at the other 3 corners so long as there is fluid in the reservoir.... but a soft pedal will be obvious from the get go.
Amazon, Napa, and OReilly (& any other parts stores) most likely don't carry brand new calipers for our vehicles. It's too expensive to reverse engineer then build calipers... especially when they are pretty specific to something like a Land Cruiser, and in OE specification if it does match other vehicles, it's a select few. It isn't like a Ford where the caliper covers 10 years, 6 or 7 models, and there are literally millions of vehicles - where a company may stand to make profit from manufacturing "new".
What that means - is that the companies they source parts from get cores (from customers, junkyards, etc) and go through and rebuild them to OE spec using OE spec parts that you would/could otherwise buy to rebuild yourself.
Usually they come with a lifetime warranty....
I have new napa calipers on my 40 because it sat for 30 years (well, to be fair I think the front axle in it only sat for 10 years). Rarely have I needed to replace calipers on a Toyota (yes, I've had a lot of them).