The seal is the pink-ish part in the photograph here on the right.
This seal is made of leather, pressed into shape.
Should you find a seal of a different material on your piston, that would indicate that the seal has been replaced at least once before.
Because the seal is made of a natural material (leather) its effective life span is limited.
Aggressive modern fuel do the rest and before you know, the ancient seal is worn and crumbles to parts.
Time to swap the seal as it is vital to the perfect operation of the carburetor.
Every time you depress the throttle pedal the piston injects a small amount of fuel in the air stream which prevents the engine from "drowning in air".
When the seal no longer properly seals, the engine will lack this small amount of fuel and becomes almost undriveable.
If you want to go the easy way, you could replace the complete piston with seal.
You can find those HERE.
But, of course, there's a price tag attached to it...
The lower-cost option is to replace just the seals.
For this purpose you can purchase the individual seals HERE.
Replacing the seals is not an easy job but it can be done by the home mechanic.
On this page, we will explain how to swap them.