I purchased a piston & nut assembly from your company,
but when I tried to install it I found a small round black sponge disk in the area of the assembly. I don’t know where this belongs and it is also ripped in half. It is about 1 1/8 inch in diameter. can you help?
Here is the parts breakdown of a GSD4030 unit
Replacement parts for GE GSD4030Y70WW | AppliancePartsPros.com
Take a look in the body parts section.
If you click on the actual picture of the part a new page will open with better views.
Not sure what you have but a couple possibilities are:
Item 555 the gasket, though using the 1 inch grid lines, it looks too big to be the part you describe.
Item 564 Piston and Nut, I do know that the early ones used a black conical gasket/seal inside, perhaps it has worn leaving you with a ripped outer edge. This would be like you describe, I would think you should be able to see the inner edge has worn badly.
Hopefully someone else has other possibilities!!