I know this doesn't really answer your question but you can buy whole new ones at most parts stores for 50-60 USD. With as ruste as those are, I'm not sure I'd trust them.
Testing them would be to check the Ohms as you move the float from the bottom to top 0 empty 90 full (one lead on that single wire the other to a good ground and don't touch and of the metal while you're testing it.
By boot thingy I assume you mean that long black mesh at the bottom of the pickup tube? I've heard that called a sock, a sleeve, or a filter. It basically just prevents large particles from going into the tube. Those get brittle with age, I'm not sure where you would get new ones.
1
