I don't think it would be theplastic links to the balls, They don't really hold the grips they only change the pitch of the blades, it has to be the little screws that hold the thrust berings in. What actually broke and what was recovered? Look and you should see where the problem came from.

Did the feathering shaft stay attached to one of the blade grips?

Did one of the little screws snap off with the end still in the feathering shaft?

Were you sure to put lock-tight in the end of the feathering shaft, if you put it only on the screwit might have wiped most of itoff when you slid the screwthrough the blade gripinto the head.

Just a thought