There are two tricks in making Camera Raw keep a new default.
You must only have ONE photo open in Camera Raw at the time you change the setting.
After changing the setting, you MUST open that photo into Photoshop.
16-bit is necessary in two situations:
1. When you're working in stupid ProPhoto RGB from stupid Lightroom. I'm very pleased to say this no longer applies to you.
2. When you're working on a very hazy photo, eg strongly backlit at golden hour or whatever. This might apply to you from time to time.
But most of the time, 8-bit is completely perfect, and 16-bit is unnecessary overkill.
And don't forget that you foolishly bought a very small Mac (hard drive size I mean) so you're going to be constantly struggling with space and performance issues. And as 16-bit files are twice as large as 8-bit files, you definitely need to stick to 8-bit as much as you can.
I'm not sure what you've been told. Yes, of course calibrators are like all electronics - they don't live forever. But as long as you treat it right you'll get quite a few good years out of it.
For this one, it should be sufficient to add a Solid Color layer of appropriate blue colour, and set that layer's blend mode to "Color", then gently mask it on to the problem areas.
You're having a run of bad luck. Fine detail like clothing fabric makes it happen.
Ah, I see the problem. Your Properties panel is too small, so you can't see the fourth field.
I've given you four numbers, which you have to put in the four fields, in the order given. 0 in the first field.
Hi Monique, I think this will work for you ...
A Channel Mixer adjustment layer, with these values:
Red 0, +101, 0, -2
Green 0, +97, 0, +1
Blue 0, +95, 0, -2
Make sure you get the numbers in exactly the right order.