Shifter boot came loose on D17

Allis D17, series 1. The boot has come loose on my shifter, where it fits around the hole in the transmission. I've been using the tractor in sub-zero weather, so I assume that rubber is very brittle and that is why it came loose. I can see where there is a lip on the steel where it fits. I am not getting it to slip onto that lip though. Of course the weather is still cold, but not quite as bad.

I know this must be fixed immediately before snow (or rain) gets into the trans.
I know this is a minor repair, but I want to ask. Does this rubber boot get stiff from age, and no longer holds on that lip? Mine does not appear to be torn or broken, but I'm wondering if I'd be best buying a new one. (They are not very costly)

Or, is there some trick I need to know, like putting a hose clamp around the base of it, to keep it in place?

One other thing. To replace that boot, I know the shifter knob must come off. Well, my knob turns, and turns, and turns, but it don't unscrew. I'm guessing there is a threaded metal piece molded into that black plastic material the knob is made from. And that threaded piece must be loose from the black plastic. The knobs are cheap, so I may as well replace that too, but how the heck do I remove the old one?

Thanks

Twist and pull up will get the knob off. It just pushes on. The boot, push down and twist. Wouldn't be a bad idea to replace the boot especially.

Even if they look good, often both pieces fatigue with age, and will rip if you try to do anything with them. Get both new, lube to install.

the new one I put on my d-19 would not stay on so I put a radiator clamp on the base of it. doesn't look so good but keeps moisture out.

Thanks for everyone's help. I would have never figured out how to remove that knob without asking. That's just a rubber slip on thing...

I did also get the old boot back in place, and ordered a new one today too. I think a big hose clamp around the base is a good idea too. That rubber must get real brittle in the extreme cold weather, and I sure dont want water getting in the tranny.

Thanks