I guess if the crash was severe enough then the valve could be damaged (i did say could! although i doubt it), was yours the yellow one that was pictured a few days ago on here?
When you were bleeding by pressing the pedal, did both sides feel the same or was one side harder to press than the other (assuming both nipples were opened the same amount)?
Were you getting a reasonable amount of pedal movement (ie easily pressed to the floor) or was it hard to press?
the same goes for the fronts.....were they both as easy to press the pedal when bleeding? were you getting the same amount of pedal movement, same amount of fluid??
Are you using goodridge type pipes and not old rubber OEM pipes??