What should I use to lubraicete the contacts on bulkhead connectors?
WET Labs recommends keeping the connectors on your meter lubricated using a good quality silicone spray lubricant, such as 3M Silicone Spray or Loctite 8021 spray. These can be purchased at your local hardware store. Avoid silicone grease. It is messy and attracts contaminants.
Do not use WD-40. It will destroy connectors.