Thanks for the thread.
Some details that Ive learned about these : I went to the manufature and they told me that the process apllied on these levelers seems to be (in french) a ''nickelage'' (from the metal ''nickel''). There seems to be a layer of nickel on these leg leveler, so they can be easely restorated to brand new by appliying a ''nickeling''.
Even if the lower moving part seems to be not removable, the nickeling process can bring the nickel inside where it's difficult to access. For example, the electrolytic ''zinguage'' (similar to a galvanisation process) don't go insides places which are difficult to access. The electrolytic process which carrys the zinc don't like to go too far. The process stops at the neares point (for example, if you want to ''zinc'' a tube, the molecules of zinc will stops before the inside of the tube and will not go inside the later, only a small amount of zinc will penetrate inside it, and only to the extremities of the inside of the tube. At the opposite, the molecules of nickel do not use an electric process to be applied. So the nickel layer can go everywhere, also inside some places difficult to access, that's why the process which should be used to restorate these levers should be the ''nickelage'' I guess.
p.s. these levelers does have rust, which explains the fact that there isn't zinc on them, since zinc would have prevent it from rust. Nickel itself do not prevent from rust (as far as I know) but permit a better ergonomy appliance. So the nickel layer looks like a thick chrome layer but it's much stronger and resistant than painting the levelers with a chrome color.