Is it all right to use transmission fluid in place of power steering for a 1990 Buick Lesabre?
No, absolutely not. Transmission fluid and power steering fluid are chemically different and have different properties. Using transmission fluid in your power steering system will likely cause damage. The seals and components in your power steering system are designed for power steering fluid. Transmission fluid can cause them to swell, leak, or fail prematurely. You'll likely end up with a more expensive repair than just replacing the power steering fluid. Always use the type of fluid specified in your owner's manual.