I am trying to find out what type of grease has the best adherence to plastic. I tried using silicon grease on some plastic guide posts but over time gravity and the slight friction action they encounter has caused the silicon grease to slide down the posts. Would white lithium grease or something else stand up better and not slide down as quickly? It's not a temperature issue, it's gravity and slight friction.

Lithium grease would be a good choice to use with plastic.

Make sure it is pure with no petroleum products in the mix.

Thanks for your response,

Why is any petroleum additive in the white lithium grease a problem? Is it because it might be corrosive or is it that it would cause the lithium grease to be more slippery and therefore more likely to slide down the plastic posts?

Petroleum products as well as many other chemicals can react with plastic in a bad way.

Labels and material data sheets may give you an idea of potential problems.