I haven't done this job on my car thankfully but I'm sure putting in some kind of O-Ring/gasket where you mentioned couldn't hurt. As for the teflon tape, I have no idea whether you applied it to a male or female fitting. Female fitting would be next to impossible to apply it to. An old plumbers trick to help put on teflon tape in tight spaces is to wrap some around the end of a pen or pencil as opposed to fiddling an entire roll around a small thread with little space to work with. I wouldn't worry about a tiny amount of teflon tape overlapping the first thread on your application and contaminating your fluid.
I would check my WIS to see if that part has an O-Ring but unfortunately the servers for most of the WIS programs out there no longer run or the software gets corrupted. (Don't waste your money on a WIS program.)
I think it would be much easier to use good quality teflon tape (Blue Monster Tape) and really try to get a good tightly wound five complete wraps (in a clockwise direction) on the thread before putting everything back together. Teflon tape is very weird if you don't use enough of it. I recently changed a water heater in my house and had a problem with one of the connections leaking. I did 4 wraps of it and water was still dripping from the threads. I took everything apart, did 6 wraps instead and not a single drop of water. I added plumbers pipe sealant on top of the teflon tape too (it can't hurt.)
If I was in your situation, I would be so mad that I'd even consider JB welding the f***er together and hope I never have a problem with the radiator again.
I would check my WIS to see if that part has an O-Ring but unfortunately the servers for most of the WIS programs out there no longer run or the software gets corrupted. (Don't waste your money on a WIS program.)
I think it would be much easier to use good quality teflon tape (Blue Monster Tape) and really try to get a good tightly wound five complete wraps (in a clockwise direction) on the thread before putting everything back together. Teflon tape is very weird if you don't use enough of it. I recently changed a water heater in my house and had a problem with one of the connections leaking. I did 4 wraps of it and water was still dripping from the threads. I took everything apart, did 6 wraps instead and not a single drop of water. I added plumbers pipe sealant on top of the teflon tape too (it can't hurt.)
If I was in your situation, I would be so mad that I'd even consider JB welding the f***er together and hope I never have a problem with the radiator again.
