Got off the phone just now with Mike at Town North
He said that when the seals leak a long time the brake fluid goes bad and becomes corrosive to the seals. So as a rule they replace the other (master/slave) while replacing the bad one. This is because sometimes the pressure breaks the old seals after the new one is put on. It saves about an hour labor since bleeding is crossover requirement. It woulda been about 250 for just slave replacement and with both it's about 350. They already started and should be done by 4:30.