I thought about the thread tape, but then it'll be in contact with the beer.
I'm pretty sure there weren't any plastic washers, although it would make perfect sense because the threads were flush before and now they are inset slightly.
I'm gonna look around for any missing pieces.
Ultimately I think I'm gonna buy a new disconnect with mfl and a swivel nut. That way I won't have to take apart the disconnect to clean the line.