How do I stop a leak in American Standard kitchen faucet?

I had a new American Standard faucet installed by a plumber less that a year ago and now it leaks from the base of the single swivel faucet lever when it is up and in a certain position. Is there a washer that is leaking or a core unit that needs to be replaced?

There are repair parts to fix this issue. Call American Standard directly at 18004421902 with model number to get correct warrany parts.