[Zeke]

I like Evaporust but it is expensive and it loses its effect with each use until utterly useless and there is no way to rejuvenate it short of straining debris as soon as possible. And that doesn't help all that much.

People have come close to duplicating the formula and it's just a matter of time. Here is an expired patent granted in 1963:
1. A RUST REMOVING COMPOSITION CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF FERMENTATION-INHIBITED SISAL JUICE SOLIDS AND N.N''-DI-(O-HYDROXY BENZYL)-ETHYLENE DIAMINE DIACETIC ACID IN A RATIO OF 1/2 -20 PARTS OF THE AMINO ACID PER 100 PARTS OF SISAL JUICE SOLIDS.

From what I've read that is close, especially the "juice" part. Beets have been mentioned many times.