"Moreover, if leaking the manual really puts the lifes of the crew at risk, would not leaking also put lifes at risk, i.e. the one of the people fighting the tanks?"

Thats the point. No military is interested in making it easier for its enemies to fight you.

And with irregular conflicts, you cannot assume everyone knows everything anyway. If you would have to fight this tank for real, don't you think, you want any information possible? Weak spots, sensors,.. or even getting enough knowledge to take over the tank. Military secrets have their reason, no matter how you judge the stance of said military.