2023 GMC Sierra 1500 — brake fluid is old but still looks clean — anyone dealt with this recently?

I'd keep this practical. Verify the cheap/easy branch on the 2023 GMC Sierra 1500 before a big repair or a big spend. That's where I'd start. Post the numbers (or the code) and people can get more specific. This is me being the wet blanket on purpose.

Write down what you already tried. A second data point from another 2023 GMC Sierra 1500 owner helps more than a generic diagnosis. Then you'll know the next fork. Did the worksheet show tax yet? If this is nothing, great. I want that in data.

Don't overfit one forum story to your car. If it still isn't clear on the 2023 GMC Sierra 1500, a specialist hour can be cheaper than another round of parts. That's where I'd start. Post the numbers (or the code) and people can get more specific. Make the next action something you can finish this week. I'm in no rush to be a hero on it.