For the trifecta (ABS, traction, brake) I have my money on the steering angle sensor... I know that for others (many?) it was the ABS unit, but in my case it was the steering angle sensor. See my post on that, it is easy to inspect (easier than having to send the ABS unit to a repair and wait to see what they say).
For finding the vacuum leak, I suggest a smoke test. It should take a few minutes to put together a "home version" of a smoke machine and to test it. I completely eliminated those on mine that way. There are several versions of the machine, I built one similar to
this one, cant find the video of the one I built.
Having said that, I think the car is a joy to drive but can be a real money pit, especially at this age...