You were right. I thought it looked like it had once had torsion springs, but by crawling inside the trunk to take a close look at the left side hinge, I found the ratchet mechanism that is supposed to keep the trunk lid up.

Naturally, it was frozen up from years of disuse, but a little penetrating grease fixed that. Now the pawl turns with a little resistance, but it doesn't come to a stop at the right place to catch the hinge and hold it up.

By fiddling with it with a fingertip I can get it to hold, then it DOES release properly when you lift the lid higher and shut it. I can probably get entirely inside so I can see what I'm doing and torque the pieces just right so they work properly.

I was probably thrown off by the stick in the trunk. Old-fashioned lid prop!

I agree that it's a bad idea to have this only on one hinge. Everything but the pawl is already on the other side. I wonder if I might remove the existing pawl, duplicate it from steel, then link the two together with a steel rod so they always work in tandem. Two mechanisms working each by themselves would tend to get hung up or out of sync pretty easy.

What do you think?