never seen this before..

this morning i was checking my clutch fluid and when i took the csp off there was a little rubber puck floating on top of the fluid. it was roughly the same diamater as the top of the resivour. i check the fluid regularly and have never noticed it. my first thought was mabe the bottom of the cap fell off but i honestly have no idea. any opinions?

 

pretty sure its normal and has always been there. its on many makes and models of cars, purpose who knows? so it seals the system if it get to low or to disperse back pressure from popping the cap off.

 

Ya that is kinda what i thought, Its just weird I have never noticed it before

 

completely normal maybe it was stuck in a nother position in the past.