Power Steering Problem

Hello Friends
I've got a 2003 Pontiac Aztec with 85K miles. Recently I've noticed a "dead spot" when I turn the wheel to the left at idle or at very low speeds--like when I'm parking. I hear a hissing noise and the wheel feels hard to turn nearing the very left extreme position. Checked power steering fluid, added just a tad, nothing significant. No leaks on the garage floor.
Any recommendation would be greatly appreciated.

Aloha
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