I would guess so Mark. That was about all that was available back then.
Capillary action is amazing it can allow dampness to travel along leads encapsulated in a solid material such as the 'Lockfit transistors'.
I can only think of encapsulation in glass as a perfect seal [valves and CRTs] but the temperature required may be a little high for the component itself.
Of course it can take years to do this, long after the intended service life of the component.
Generally that is.. John.