I love these boots and have gone through multiple pairs over the years, most recently, retired my last pair after getting back from Kilimanjaro 2 weeks ago.
I never sealed them... but have always waterproofed them multiple times over the years. Get some Nikwax and that should do the job. Doesn't last forever so depending how much use they get, may need some reapplication after a while (i.e. I do mine twice a year).
They don't have a gore-tex liner, but doesn't mean that if you step in water even without sealing or waterproofing them they'll leak right away. They're very well built and they do keep water out.