This OP is really a reminder as to one of the reasons the Halachos of LH l’toeles are so specific and detailed. Among the 7 prerequisite conditions for being allowed to speak l’toeles is that one must have FIRST HAND KNOWLEDGE of what one is speaking about. Hearsay, even from a very reliable source cannot be repeated, even l’toeles. (of course for questions l’maasah, consult your LOR).
Just as a reminder, the other 6 conditions are:
1)you were dan lkaf zchust the person in your own mind
2)you made every attempt to solve the problem by going to the person directly rather than involving someone else
3)you do not exaggerate or offer your opinion, but simply repeat the information with 100 % accuracy
4)your intention in repeating the LH is only l’toeles, with no other ulterior motives
5)there is no other way to accomplish the same goal without saying the LH
6)no undeserved harm will come to the person you are speaking about
This is just an outline — it is a good practice to always ask a shailah if one feels there may be a need to repeat negative information about someone.