It has been already mentioned a few times that the (now ex) Pilot and Instructor of Ethiopian Airlines Bernd Kai von Hoesslin has expressed concerns regarding the training and operations of ET in general and specifically the MAX BEFORE the ET crash. Some excerpt of his bloomberg interview ("Expat Pilot Turns Self-Styled Whistle-Blower After 737 Max Crash") from mid August has been posted here a few days ago.
What seems to be less known is that von Hoesslin has posted on youtube a series of videos and audios (secretly?) recorded while he was still working for ET.
One example is a 13 minutes video of various "interviews" with ET pilots regarding the post Lion Air crash MAX's AD, where it appears that most pilots had very little knowledge of that AD.
The tiny number of views (few tens) this videos and audios have on youtube suggest that so far they have not been noticed.