At this point, I would not worry about mixing brands. If you want to try sealant, that is OK. It is not good for seals, but at this point it won’t hurt anything that doesn’t need replacing anyway.
ATF is cheap. Just toss some old cardboard on the garage floor to catch the drips and keep adding fluid until you are ready to get rid of the car. I would not worry too much about a catastrophic failure. It is unlikely, and I once drove a Corvette with failed power steering from Omaha to Denver.
FYI, a remanufactured rack and pinion for your car is about $350. If you need all new hoses (likely) that is another $250, plus about $300 labor, a few odds and ends, and you should be looking at not much more than $1000 total if you were to fix it.