Slickoleum Light Grease (aka Slick Honey, like SRAM butter)
Slickoleum Light Grease is the king of all mountain bike seal greases. Mechanics use it for fork seals, shock seals, dropper post seals and even as a freehub grease.
Fun fact: SRAM use slickoleum to manufacture their very similar product: SRAM butter. But that costs about $20 for an ounce. Why not get the original at a better price?