Thanks guys, I'll do some thorough cleaning.

Thanks Mike,
No, I didn't center with the pedal during reassembly. I typically eye-ball the advance screw and cog wheel, and try making the shoes as equally advanced as possible before sliding the drums on.

Final manual shoe advance was done with the drums on and that's when I would get in the car and check the brake pedal felt reasonably hard.
I think I'll repeat the shoe advance adjustment process.

And thanks - I'll check for any unusual wear pattern on the pads.

A condition that could cause my symptom is if three-of-four brake cylinders were sticking every time the car sat for 10+ hours. The one "good" cylinder gets all the pressure the first time, then the other three cylinders become unstuck after the first applications of brake and they all work fine after that.