A washer in a Sig P220?

It's been years since I've attended armorer's school. A friend removed the trigger and installed a short trigger. It works. He notices a rubber washer (not from the grips) that fits on the pivot pin (located on the decocking lever). While it fits there, it doesn't really have room. So, anyone know where it goes?
 
It's been years since I swapped triggers in a 220, but I sure don't recall there being any little rubber washers in there.

I guess it's better to put a washer in a P220, than the other way around;)
 
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