Mansfield Dual Flush Valve Tower - 308DF3

Where can a person buy just the clear silicon gasket that located at the bottom of the tower?

Does this work with the button on top of cover

How do you remove the valve tower to either replace it or the seal?

How do you adjust the flush level? My full and half flush are both at thr top of the tower/set to minimim flush, which simply isn't useful. Please hel