Thanks for posting the pic. My unit has very similar plumbing. Most of the fittings are copper and the grey tubing is connected to the fittings with a copper band. Unfortunately it must take a special tool to remove and reinstall those bands. Also, unfortunately, my winter drain valves are made of a plastic material. I noticed that the small in-line sediment filter close to the water pump is connected to the tubing with stainless screw clamps. I cannot tell for sure but looking at your picture I believe yours is connected the same way. Perhaps I can buy a new shut off valve and connect it to the tubing with screw clamps.
I have learned much and am very thankful to everyone who responded. One thing for sure, I will get some spare fittings and hopefully be ready for problems in the future.