Well as usual my bad luck has risen yet again the head of this sensor has snapped off leaving the rest of the sensor in the thread. The unit is well tight in the thread i think that a thread lock material may of been used and with the unit being plastic it was just too tight for the head not to break. The o-ring seems ok so why it was weeping i don't really know. I have mentioned before that maybe it was coming through the unit itself as where the electric connector would fit in was always damp with fuel. Anyway i have a bigger job now and am a bit stuck as which way to go. Just couldn't unscrew could it oh no. Thanks.