I'm not familiar with the e-less therefor, stales. But my own pet peeve with this similar situation is aging/ageing. In fact, there was an interesting thread about it while you were away that might offer some interesting discussion and insight into this sort of dilemma:
http://wordsmith.org/board/showthreaded.pl?Cat=&Board=words&Number=38999
Now, I'll have to look into this therefor/therefore thing!