car rear brakes

yes...the caliper slides may have been cross threaded~. lift up the wheel, take the tire off and see if you can move the caliper in and out a few millimeters...if seized will show uneven wear on the disc rotor and will not stop the car evenly...and apparently in your case will begin leakin'~....yes, take it back and stick their nose in it...worked with my BAD dog..."look what you've done"~

inspect all components at the wheel....they left a major nut off or cross- threaded something under there...push and pull and check how much play there is and note the condition of the caliper~ on some models there is a Parking brake inside the rotor~ perhaps yours is like this....most likely the rear brakes are like this...you might check the operation there~

fluid loss may cause spongy brake pedal, if not bled at that wheel,final step is to adjust star wheel up to slight drag on new shoes, that's whats missing no doubt, no biggie I'm sure he's as good as most real mechanics