Brake Disc Caliper problems of the 2008 Lincoln MKZ

Brake pedal goes all the way to the floor, vehicle increasingly difficult to stop after abs event. 11/10/18-dealer performed diagnostics indicating rear rotors need replacing, authorized repair. 11/10/18 after replacing rotors dealer states rear caliper action is erratic, states rear calipers need replaced due to erratic action. Authorized repair with oem Ford parts, not available until 11/12/18. Dealer vehemently denies hcu is the issue even after I propose this scenario. States not the hcu 11/12/18-dealer called said pedal is much better, however, although there are no indications or codes, hcu is faulty, wants me to pick up car. States that pedal travel returns, but might want to have the hcu replaced. !! dealer previously stated hcu was not the issue, the rear calipers were: due to erratic behavior. Service to this point to have components replaced, that have not resolved initial complaint vehicle was previously involved in frontal crash from previous owner. Details were not immediately available to me. Will be requesting dealer assistance with part replacement in this scenario.

Car was moving hit bump in road and brake pedal went to floor. Thinking problem was brake pads and calipers had front and read pads and calipers installed still low brake pedal. Went to Lincoln dealer had brake flush preformed by Lincoln dealer,report came back it was my hydraulic control module costing $1,306 plus tax labor is separate cost. Had car appraised at Lincoln dealer I brought car from apprasil came back $ 3,300 dollars. Part is half current value of car. Still paying for car . Car was priced at approximately $7800. In the first year almost starting second year of 4 year loan. Feeling very helpless also dealer who preformed brake flush and diagnosis says car is unsafe to drive have the results from dealer in writing.