Had this issue with my BX. Don't know how similarly the B-series is set up but I can tell you one thing... it was a real pain to fix (sorry to be the bearer of bad news). I replaced the o-rings initially and it slowed the leak but eventually I had to replace the bushings pressed into the axle housing which had become wallowed out. There is no easy way to drive out the bushings. They had to be split, edges curled inward, then pulled out. I ended up dropping the axle and taking the entire thing to a local shop to do the work. The good news is that it fixed the leak and I did not have to replace the pivot pin (mic'ed it for roundness). Unfortunately from what I hear, I'll probably end up doing it again every 500 Mrs or so.