How many miles on scoot?
Cutch wear?....as the clutch wears the clutch's slave cylinder's piston mover farther out thus needing more of the hydraulic fluid to fill the space. You can have the same situation on the brakes as they wear and the caliper piston move out... more fluid is needed to take up the space.
Fill the reservoir and watch the level to make sure it is not going out like a leak somewhere. I believe it is also possible for the clutch slave cylinder fluid to leak into the engine so you might not see any fluid dripping.
Please let us know what you find.