Help with Radiator Leak Where Tranny Line Goes In

2000 XJ 4.0L Automatic w/ A/C

radiator replaced 1.5 yrs ago. just developed a leak at the radiator where a transmission line enters it. its drivers side just under where the radiator cap is. i took out the air filter housing, detached the tranny line, took out the brass adaptor piece that has female threads on both sides (one side rounded for the flare in the tranny tubing) and tightened the larger flat nut and washer. i put some teflon tape on the brass piece and reinstalled it and the tranny line.

it seems that it wants to leak either where the brass adaptor piece threads into the brass piece coming out of the radiator or where the large flat nut and washer go against the radiator. i am leaning towards it leaking from the radiator / large nut area.

my question is if there is supposed to be some sort of gasket/washer behind the large nut and washer against the radiator? i am scared to really wrench down on that nut being that its going on a brass thread against a plastic radiator.

i drove it around the block and it seems to drip a little less but still leaking.

any thoughts?

Mine is leaking where the brass? adapter screws into the big nut thing against the rad tank. I have tightened it but I am afraid to tighten any more. I'll have to take it apart and try teflon tape. My radiator is a mopar replacement only a few years old. It's not leaking bad, maybe and a pint of coolant every 2 weeks.

teflon tape should help.