teflon tape

97 TJ 4.0L So I swapped out my leaky radiator from extreme terrain. Same radiator. Same fittings. The old o rings/gasket where torn but did not leak. I put teflon tape but no o ring in the new rad and now it is leaking. Do they typically have an o ring and teflon? If so anyone know the size?

Am I correct in thinking there should NOT be a need to use teflon tape on *this* connection from my tank to the regulator? There *IS* a hard plastic washer/gasket in the regulator itself.