I have a couple of 60's car radios by mopar containing rca germanium transistors, rca made a batch, a very large batch of 4 pin trannys where the sticky goop inside the transistor etches away (slowy over 40 years) at the junction and destroys it.
That is just what I heard, the above description might be the actual reason, I wonder if bulb bopping would fix ingrowing whiskers?
Vibration can also cause failiure, the whisker lets go, but I think you'd need to be severe to do that.
So long as the junction temp doesnt go over the max specified in the datasheet it should work for years.
I'm with nige, you can still get ge junction diodes for rectification, switching and probably a load of other uses.