Maybe the weak stock twins when pushed past 18psi? Leaking ECU capacitors? Not many significant things I can think of.
Valve cover gasket leaks.
Crank pulley as someone mentioned.
Valve stems as mentioned as well, but I think most owners just ignore it.
I've seen a crank walked 2JZ before and many owners on the forums post about it. It probably applies to 1JZ as well just haven't heard or seen one yet. Disable the clutch switch.