I was topping off the clutch master cylinder on my 1992 Civic VX HB with fluid when I saw this plastic disc-like part float up from inside the reservoir. My mechanic doesn't know what its for and removed it. Does anyone know?

 

It is a float for the clutch master reservoir.

 

Put it back in the clutch fluid reservoir.

 

@Ryanthegreat1 What is its purpose?

 

Visual aid for fluid level inspection.

 

Okay, that makes sense. Thank you!