You pretty much answered all your own questions! Yes, you need to rescue the rookie, get that item he gives you, and you need to use it to pass the 'paralysis' thing.
And yes, that item does expire when you leave the forest, so you need to do it before leaving. And yes, there's a way to 'recharge' that item too.
I've already started a new game where I did dispel the rune and gotten the fireball spell. I'll just have to use that file then. If the fire spell really is that useful later on. Otherwise I'm currently travelling south in pursuit of the other travellers. Fighting slugs now. But I'm running in error readings a lot more often now.
