Well did you make sure your front brakes wer'nt worn as well?
Did you make sure the brake pad sensor was plugged in?
DON'T USE ANY OIL ADDITIVES OTHER THAN TOP GRADE ONES YOU CAN'T FIND AT THE STORES!!!
There are many reasons you can find why not to use them if you search.
You can find out by going to:
http://www.bobistheoilguy.com/