By looking at your previous posts this car has been pretty neglected prior to your "gallant" efforts. You need to take it to a dealer & have them do an InspeectionII done to it.
I'll forwarn you, it won't be cheap $$$ but it will address all your issues and you'll have a warranty on the work performed. It'll be money well spent.
Re: your brake issue - you're talking a safety issue - a master cylinder is nothing to messed with if you're a novice. (bleeding and pad replacement are good for DIYs) but with all the issues this car has have the Inspect II done. You'll have a "ground zero" starting point - then keep accurate records. You'll enjoy the car more and spend less time playing Sherlock Holmes attempting to diagnose the next problem.