My kit y-axis idler started making clicking noises, so I wanted to replace it with a (hopefully) higher-quality alternative. I could only find 9mm, 20T GT2 idlers with a larger OD (18mm, instead of 16mm) and 13mm length (instead of 12mm) purchased from Zaribo in the UK.
https://zaribo.com/pulleys-belts/404-9mm-gt2-20t-black-idler-pulley-toothed-2gt.html
This is a simple remix of the stock y-ider block modified for this idler.
I printed it in ASA, and just realized I forgot to scale by 100.5% for the higher shrinkage. Still worked out for me, although the fit was a little tight.
The author remixed this model.