Drain it all out and put in a better quality fluid in! Synthetic is my preference. just kidding. If i were you i would get the Lucas Power steering stop leak, it isnt just for leaks. add it as a topper.
I found my Cadillac dealer parts department to be open today but when I gave him that part number he couldn't find it, like it doesn't exist, even when GMPartsDirect.com clearly shows it. Some more searching online finds another part number for the same product but in a larger bottle which the dealer does have. I would think the parts people would know this! Instead I had to make 2 trips.
Also, if you're still uneasy about the number difference, look for a fluid that says it meets "specification 9985010," which is the document that describes the performance characteristics of PSF for service in GM vehicles. A lot of aftermarket fluids mention this specification.
I looked in to it, GM has different part numbers based on container size, for the same product.
If you note on the page, both the assembly lube and the Dex VI have the same four beginning numbers, so those aren't the identifiers. We can also see that the last four numbers change on the PSF with different size containers, so those aren't identifiers. In fact, the numbers being quoted likely aren't specifications, they are simply part numbers (and relatively arbitrary from a compatibility point of view) . I'd propose that any GM compatible PSF would be fine. Seriously.