Alignment of the rotor is critical for these gearbox to work.

Notice that there are 2 "T" Labels on the T rotor, and same with B rotor with "B" Labels

One "T" is on the Tooth and the other "T" is in between 2 Teeth, This is also the same with B rotor

Make a Sharpie Mark in between the teeth of "T" Rotor Where the "T" is Labeled

For B Rotor, Make a sharpie mark on the tooth where the "B" is Labeled.

The Correct Alignment will look something like the Third Picture