Mike Sanders Grease. German car magazines rate this stuff with the highest score. I only have experience with their 'grease strips': you put them between fenders and body etc. My Saab has them installed since 2011 and not a single sign of rust. Which is remarkable: the '70s Saab rust like an Alfa Sud.

https://www.scparts.co.uk/en/worksho.../mike-sanders/