I use Aero Kroil for penetrating oil. Works better than PB or liquid wrench. But it may not be up to the task of rusted brake bleeders. It's worth some trouble to avoid breaking them off (far too easy to do). I would assume you need to overhaul the wheel cylinders and just take them off the truck and put them in the bench vise then you can get them as hot as you need to with a torch to get the bleed screws out. If you do break one off there exist reverse-twist drills (Snap-on, among others) so you can drill it out and hopefully the bleed screw will begin to turn with the drill before you hit bottom.
On my hydro-vac there is a large hex cap at the end of the cylinder with a bleed screw in it. Un-screw that, heat it and remove the bleed screw. I would not heat it in situ. Otherwise I'd put the hydro-vac on the bench and go from there. Cardone sells remans for a coupel hundred bucks exchange. You can also buy parts but I haven't researched where lately.
A pressure bleeder will make bleeding the hydro-vac much easier otherwise your pedal person will get bored and testy and claim to have pressing things to do.
