My steering was really groaning badly a few days ago, especially at slow speeds and when the engine was cold. I finally checked the PS fluid resevoir, and it was very, very low. Took more than a pint to get the fluid up. I'd just filled it a couple of months ago, and am mystified at where the fluid went. The steering still groans, especially at slow speeds, but not as bad as it was a few days ago. I'm not noticing any big obvious leaks, but this fluid obviously got out somehow. And the continued groaning concerns me.

Question: have I likely done serious damage to my PS pump? Or does the system just need to be bled out somehow? Any recomendations?

First you need to find the cause of the leak. 240 power steering systems can leak at the ends of the steering rack. Pull the belly pan and look for signs of fresh fluid. Look inside the rubber bellows - they should not be saturated with fluid. Check the two fluid hoses and their connections at the rack and the pump. Note that a leaking hose will drip fluid all over the driver's side rack boot and, at first look, will appear that the rack is leaking.

Fix the leak and follow the instructions in the FAQs for bleeding the system. Doubt you damaged that Saginaw pump, as they have a reputation for toughness.