Water leak around shut off under the floor, *See ic)

I'd suggest to first determine exactly what's leaking. Tissue paper positioned close to the pipes will help to determine that.

I'd suggest to use a Sharkbite valve/fitting combination for replacement. You will need to cut/grind those band clamps off the existing pipe to remove the valve. Removing the clamp with the phillips head fastener will probably help when working on this.

There are many you tube videos , just type in your search box

PEX Tube How To Cut Off Crimp Rings Without Damaging Fittings video

This has already happened to your rig - that's why the other valve is white. I would replace the black valve with one just like the white one. That will be the easiest and is a good fix but you will have to surgically remove the two copper bands.
The bad and good; you have Qest tubing (NOT Pex) which has a sorted history. The tubing itself is great but the terminations are troublesome. However, you do have the better, copper crimps instead of the horrid aluminum parts.
The white valve uses internal compression to seal and will work better than what is there. Any RY parts store will have the white valve, just take a pic of it to show them. This white valve will be for Pex tubing but will work fine for your Qest lines

Dremel tool with small cutting wheel.

ScottG wrote:
This has already happened to your rig - that's why the other valve is white. I would replace the black valve with one just like the white one. That will be the easiest and is a good fix but you will have to surgically remove the two copper bands.
The bad and good; you have Qest tubing (NOT Pex) which has a sorted history. The tubing itself is great but the terminations are troublesome. However, you do have the better, copper crimps instead of the horrid aluminum parts.
The white valve uses internal compression to seal and will work better than what is there. Any RY parts store will have the white valve, just take a pic of it to show them. This white valve will be for Pex tubing but will work fine for your Qest lines

X2 The white valve is a Flair it fitting, they work great. Ace hardware used to sell them. I used a hacksaw blade to cut a notch halfway thru the copper band and used a slotted screw driver to twist and snap the band.
Flair it clickey