I'm so sorry you are having such a problem with your Buick.
We have had extremely good luck with 3 Buicks in a row. Two Park Ave's and the latest one is a LeSabre.
We gave our son the first one when we got the next one. He drove it until it had about 200,000 miles on it. It was a 1989. His son finally took the transmission out when he started driving. (Why do boys always do that?? This was an automatic transmission too!!!)
We are still driving the second one. Left it here (Florida) when we left last spring. It has almost 140,000 miles on it. It is a 1994. Things are starting to "go" such as the automatic pull-down for the trunk (they don't even put those on anymore), and the battery was dead when I got here.
No trouble at all with the LeSabre yet but it's "young" - 2003.
I'm am really sorry you are having such a hard time. Auto's can be a real pain sometimes.
Here's hoping you can get going on Friday with no more hold-ups.

Shirley