I did not invent this technique. Last week Al Osterud, a veteran Marx collector of many decades, shared a technique for removing and installing Marx coupler springs without the skills and steady hand of a microsurgeon.
All you need is a piece of 1/8-inch K&S square tube, which resembles the tool Marx used to install them at the factory, and a toothpick or a straightened paper clip. Marx wouldn’t make anything that wasn’t easy to put together, which made its couplers so maddening to work on. Why was it easy in the factory and nearly impossible at home? With the right tools, it is indeed easy.