That's a crack. Whether it occurred during manufacture or later when it was running is anyone's guess - probably from cooling when it was cast. The EA82T heads are prone to cracking into the cooling jackets though if pushed hard. I wouldn't run them particularly hard. Anyone that has attempted more than 150 WHP from the EA82T has not had it last long. They just weren't up to the task. Properly setup and monitored though they can last a decent amount of time at stock power or slightly over - 120 at the wheels for example. The biggest problem is now the lack of parts and the frustrating complexity of the whole assembly compared to an EJ that can quadruple their performance with ease and are much simpler overall without the tendency toward ticking lifters, cracking heads, etc.
GD