Another lull in other house-moving business allowed me to quickly saw up a slat into the right sizes, drill holes in the runner things, and file off the pointy edges. And screw them into position! Even though the bit where the drawers go doesn't get a lot of sunlight, there was clear enough colouration to see where the old runners had been.
Damaged runner and improvised replacements
Three missing runners
It was done rather quickly! So when I set up the desk in the new house, I can welcome it to a new phase in its life! Always satisfying, keeping something old going. I've had that desk since my Amsterdam time! And now it's ready for a Bethesda period!