To know for sure, you need to identify the transmission type (e.g., Hydra-Matic, Powerglide, etc.) Then, you can research the correct fluid for that specific transmission. Your best resources for this information are:
* The owner's manual: If you have the original owner's manual, it will specify the recommended transmission fluid.
* A Pontiac parts catalog from 1957: These catalogs often list fluid specifications by transmission type. You might find digital versions online.
* Online forums dedicated to classic Pontiacs: Enthusiast forums often have experienced members who can help you identify your transmission and recommend the proper fluid.
Using the wrong fluid can severely damage your transmission. Don't guess; take the time to find the correct information before adding any fluid.