My vintage Peugeot bike came with Weinmann brake levers which have plastic adjustment barrels. Like these (not mine).
Mine are pretty beat up. I can still find some on eBay, but for $25 + shipping. Which seems like a lot for these plastic things. So I designed a 3D model:
And 3D-printed the version. Looks good! Just needs some minor adjustments, and I'm ready to print them for real!
I'll share the final design on my thingiverse profile.