I have been having braking issues of 1 wheel locking up. I replaced the hose and the caliper twice. I flushed system with new synthetic fluid and its still sticking. I went to remove the cap to add some to the reservoir and the rubber inside is swollen as if oil of some type got into the system. I have no idea how it could have but would I still need to replace entire system or just what goes to the one wheel that's sticking?