2003 Kia Rio sticking Brakes

In your reply, please use punctuation, otherwise that huge sentence can be read multiple ways, and you know I'm going to read it wrong. The flex hose is the most likely suspect, but since that has been replaced already, I'm worried that the next most likely cause is brake fluid contaminated with a petroleum product. The next time this happens, stop on a slight incline, shift to neutral, place a block about a foot downhill of one tire so you won't look funny chasing after the vehicle, then use a line wrench to loosen the steel lines at the master cylinder. If brake fluid spurts out and the brake releases, there's three possible causes. The brake light switch could be misadjusted and is holding the brake pedal down an inch or two, the power booster may have been replaced and has an adjustable push rod that is adjusted too long, or the brake fluid has engine oil, transmission fluid, power steering fluid, or penetrating oil in it. That is going to be a real expensive repair.

A quick test for the first two causes is to loosen the mounting nuts where the master cylinder bolts to the power booster. Slide the master cylinder away from the booster about 1/8". If the brake releases, contaminated brake fluid is no longer the main suspect.