After a long time of trying, I have finally managed to obtain a 1928 Sheaffer Jade Radite Flattop. It has been my experience that side lever sac filled pens are difficult to thoroughly flush. I have also been told that the Noodlers Inks that I favor are not good to use in an old pen like this. So I must choose one benign ink and stick with it. I assume that there will be residue of ink in it that will initially affect the color of what ever I put in it, but I also assume that if I persist with my chosen ink, it will eventually become dominant. I have seven differnt bottles of Herbin, which I believe to be the mildest amd least offensive ink. I also have a variety of Noodlers, which I think I must discount. In addition I have several Skrip, Mont Blanc, and Pelikan. I do not really want to fill it with black ink, because my Waterman Persian is my black ink pen, I use Skrip black in it. So to help me decide, I want first to decide if I should be concerned with how benign the ink is, and from that choose a manufacturer, then having done that I will choose a color for it.
The ink will effect the sac, the feed and likely part of the section during filling. Modern inks are certainly far less corrosive than ANY ink that was available in 1928. The biggest threat to the color of your jade pen will be the sac itself outgassing and there again, modern sacs will be far less a problem than what was available in 1928.