Yamaha YK-X Series User Manual page 141

Apply grease to entire oldham coupling.
Fit O-ring (supplied) into this groove.
Apply grease to sufficiently fill in the ball space.
Never remove these temporarily tightened bolts.
The axis will otherwise deviate from center.
Fig. 5-7
5-19
CHAPTER 5 Periodic Inspection
Wave generator
Apply grease to entire inner surface to
the thickness equal to ball diameter.
Flexible spline
Circular spline