For single lead sensors, we like to use Copslip ( probably didn't spell it right ). It is an antiseze that has small copper balls in it and when conpressed between threads, aids in conductivity. IT IS NOT a fix all. but I have seen some changes in readings between the sensor and ground by using it.
If you are challenged with a sensor that seems to be giving you problems, maybe a little of this would help.
Riock is right about the screens.
Hope this helps.
