As you mentioned, the first place to start is servicing the transmission with a new filter, gasket, and use Dexron VI (6) fluid.
While you are under there, I would have some spray electronic contact cleaner handy and compressed air, & consider removing the transmission electrical connectors. Look for PS fluid residue/ inspection.
Did you power wash after the PS hose broke, where water could have into other connectors as well?
I dont know where all else that high pressure PS fluid is, but if it did get into connectors, cleaning may help.
Of course once the new fluid and connectors are checked & clean, it may be worthwhile to use a shop scanner and check for any history & stored codes.
It may point to some PCM codes that may be helpful.
1997 Buick Pk Ave (Soft Ride) Suspension!