I swapped my front drums out for Disc's many years ago on my 60 Dart. May have used synthetic fluid at the time but don't remember. Recently checked the fluid and added some dot 3. Now my brakes are locking up after a short drive. I suspect the new fluid is not playing nice with the old and swelling up. I plan on purging out the old fluid until I get new clean fluid at each wheel. My question is, will that cure my issue or do I need to flush the system?