If you see rust, corrosion, or a cracked valve body, you may need to replace the entire manifold assembly. That’s a bigger job—think season two of a Netflix binge, not a single episode. Don’t be a hero; some battles are for plumbers.
Also, if your system uses high-pressure steam or hazardous fluid, step away. That’s a job for people with certifications and insurance. No shame in knowing your limits. Knowing your limits is a superpower.