another point with *cartridge sealed* bearing hubs: the outer race is usually a tight press-fit in the hub shell, and the axle is firmly held to the inner race by the friction of the so-called "cone" because that's what makes the rotating action taken completely by the ball bearings. If the cartridge pops out of the shell as easily as you say, I think the hub shell has worn to the point that the cartridge itself can spin...which defeats the principal. Your hubs may not be worth rebuilding if that's the case, and continued spinning will just make the wear worse. If you want to save them I'd try LocTite GREEN for the outer races/hub contact, if the wear is too much for that maybe an epoxy like JB Weld.