o-ring for coolant sensor giving me problems

[brooch]

I just replaced the radiator in my M50 engine, however I am not sure where to locate the o-ring for the coolant sensor. I removed the old one and didn't see an existing one. I inserted the o-ring over the sensor inside the plastic nut, however I can't seem to thread it on to the radiator after doing so. Am I doing something wrong? Is there supposed to be a slot for this o-ring inside the nut or do I really have to force it on to get the thread started? For those of u that have done this, your input is greatly appreciated.

TIA,
Brooch

1991 525iA
M50

[shogun]

check here, explosion view detail drawings
http://www.realoem.com/bmw/select.do?PHPSESSID=2f576ced29477680ec938848d4d39e a1

[brooch]

check here, explosion view detail drawings
http://www.realoem.com/bmw/select.do?PHPSESSID=2f576ced29477680ec938848d4d39e a1

I have seen that diagram, but it doesn't really tell where the o-ring goes. It could either be inserted inside the plastic nut where I can't seem to get the thread started or inserted over the threaded part of the radiator which I haven't tried yet. Not sure which one is correct.

[DaveVoorhis]

Push the o-ring down inside the nut. When properly positioned, it won't interfere with the threads.

[brooch]

Push the o-ring down inside the nut. When properly positioned, it won't interfere with the threads.

thanks Dave, so I take it there is a slot the o-ring sits in or does it just sit at the bottom face of the nut? I tried threading the sensor with the o-ring sitting on the bottom face of the nut on my old radiator that I replaced and I couldn't get the thread started. I wonder if I have the correct o-ring? Its 2mm in diameter and it fits over the sensor tube properly. Guess I'll give it another go.

[DaveVoorhis]

The o-ring sits at the bottom inside face of the nut. When properly placed, it holds the nut to the sensor but the nut spins freely.