Do I need to apply grease to the spline of the disc?

Yes, it is required.
However, depending on the method of application and the amount, applied grease may disperse, causing judder and bad disengagement.

  1. Apply grease evenly to the spline tooth surface of both the main shaft side and the disc side using a brush or similar.
  2.  After the application, insert the disc into the main shaft, and slide it to see if it will move smoothly.
  3. Wipe off the grease straying out from the disc and the main shaft using a rag or something.

Be careful not to deposit any grease or any other oil on the friction surface (flywheel, P PLATE, IM PLATE, disc). It may cause judder, slip, etc.