ACF-50 or Corrosion-X
Do not use WD40 it cracks plastics over time WD 40 is a lubricant.
When the inside of a connector is sprayed with WD 40 and reconnected contacts will have a higher resistances, its like having oil on your contacts.
Spray ACF50 in your connector and there will be very little change in the resistances of the connection .
Protecting the inside of a connector should be don with DC 4 compound , the outside of a Cannon plug can be protected with ACF 50.