Saturn SIB rear drain??

[sidecar]

While trying to find a water leak, I removed the rear drain and saw that the backflow diaphragm was shrunk and cracked. Does anyone know what these things are called or where I can buy 1? I'm thinking that this, along with a poor fitting plug may be where the leak is. Thanks for any and all responses

[jeffstevens763@g]

Mushroom valve

[sidecar]

Thank you, my friend...