I started from the nanokontrol2 fader Cap uploaded by xantharian and I made a couple of simple changes.

Be reassured, these fader caps work interchangeably on either version of the korg nanokontrol (1 or 2)

Print instructions

Category: Audio Print Settings

Printer Brand: Prusa

Printer: I3 MK3S

Rafts: No

Supports: Yes

Resolution: 0.15mm

Infill: 15%

Filament: Generic PLA PLA Gray
Notes:

Instructions for printing:
Lay the fader on its sidewall. Use a brim to ensure good first layer bond. Add support material only for features directly above the bed (the two studs)

Use 2 perimeters, 15% infill.

The samples in the photos were printed using the included gray PLA that came with my Prusa Mk3s

Post-Printing

The support breaks off easily with a pair of needle nosed pliers. The caps fit tightly over the fader, but to press them in, start with the cap rocked to one side and, while applaying even pressure, rock it in the opposite direction and it should pop right in and hold well.

How I Designed This

First, I cleaned up the original stl file since the meshmixer reported having some errors when I opened it.

Then, I removed the ridges on the vertical walls because those aren't really necessary, and once those surfaces are flat, we can use either of those walls as the bottom layer, requiring support only under the studs. You might have noticed that the original version of the korg nanokontrol did not have vertical ridges on the sides of the fadercaps.