On p. 97 of Alpha Strike Commander's Edition, it states, "...In addition, the Human TRO may look for a weak spot in a target unit once per game..."
I read this as the Human TRO may use this ability more than once per game, but only one time for each new target. So, if the Human TRO has already used the ability on a Raven per se, then the Human TRO could not do so again in the same game, but could use the ability again on a Panther. Would that be the correct interpretation?