Help confirm where to fill top reservoir please.

Greetings

I have a 1964 Dart GT convertible, and want to confirm the level of fluid in the top pump reservoir. They guy I bought it from (4 or so years ago) said it likely needed more fluid. The top mainly stays down and the up/down motion isn’t too bad/slow. Sometimes I feel I need to help it when going up. This being said, I have no idea what the correct speed is either. Could be that it’s working perfectly.
Anyway, I’d like to confirm where I check and add more fluid. On the passenger side of my pump there isn’t a slotted screw, but rather a rubber grommet. Is this what I need to pop out to check/fill?

thank you very much,
Greg

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