Brake Master Cylinder Pushrod Issue

[Mike1261]

Looking at a video on YouTube, apparently there's supposed to be a crown shaped washer on the brake master cylinder Pushrod.

I suspect this washer fell into the brake booster itself upon removal. I have the Pushrod and the little metal puck thing, but can't find the washer thingy.

1. Can I replace the washer thingy easily? What's it called/part number?

2. If the old one fell into the booster (at the front of the opening there's a spring and a gap), can it stay there harmlessly or do I have to pull out the booster?

3. Is there a photo or diagram or video somewhere of how the Pushrod goes back into the booster, orientation of the little puck thing, etc?