No, absolutely not. Transmission fluid and power steering fluid are completely different fluids with different properties. Using transmission fluid in your 1991 Buick Regal's power steering system will likely cause serious damage. The seals and components in the power steering system are not designed for transmission fluid, and it could lead to leaks, pump failure, and potentially even damage to the steering rack.
Always use the correct power steering fluid specified for your vehicle in your owner's manual. If you are unsure, consult a mechanic or auto parts store for assistance.
