Getting the sprocket on the motor to fit snugly, but not too snugly, on a calibration aid was a bit of a challenge for me.
When I was setting up my Maslow, I didn’t have a 3d printer but did have access to a small cnc router. Here’s the part that made to find 12 o’clock that has a snug fit: Easel Link. The part is based off the info in this Maslow forum thread by @c0depr1sm. I modified the hole for the level to fit these vials from Amazon.
I also looked at these calibration aids on Thingiverse, but didn’t have a 3d printer at the time, so I can’t personally vouch for their fit.