Pros and Cons of Types of "Dielectric Grease"
Sounds like those big old Canon circular Mil connectors.

Nyogel 760G looks like a good solution. It's a synthetic organic oil or "non-oil" with carbon-pairs between two H molecules.  It is slippery, low viscosity and clean (when no dust is present) with low evaporation rates, good antioxidation qualities and good water rejection qualities , yet thin enough to make easy electrical contact frpm surface roughness.   However, Silicone is added just as a thickener and being an insulator both electrical and thermal would be a poor choice ( unless lots of contact force, roughness, ie. poor quality not ARINC quality)  THese oils are generally low k factors less than or equal epoxy in FR4 and thus betterinsulators than air if clean but any liquid is worse than air with leakage R from conductive dust easily mobile and chargeable. (e.g. salt spray would be worse after drying) 

Water on the other hand is 20 ~30 times worse with a k factor of 80 for capacitance but like oil better for insulation unless contaminated.(than air.)  

Any Moisture + dust can be a a leaky stray capacitance, but oil is better than water and dry air with dust is better than anything wet with dust and wet with salt is worse.

Your finger on the board can tell you is a circuit is too sensitive and lacks conformal coating or solder mask or gaurd tracks. Interface connectors have no business being high impedance. SO source at either end must be low impedance and if floating at least low common mode impedance Cap to ground.

If there are no critical stray capaitance circuits using &lt;50pF caps (light  dry fingertip), then a silcone spray conformal coat is a good insulator and thin renough to reduce pF /cm2  then the Nyogel for external contact lubricant or even WD40 thin spray or apply with  a soaked plug inverted.