the first time i worked up brahms 2, i did so using the bowings from the zimmerman book and it was nothing short of a revelation. it really opened up the part for me and illustrated the genius of brahms. at first glance, there are a few weird decisions he seems to have made, but if you stick with it you'll realize how great the part feels in your right hand; the whole thing flows. last i checked, these bowings are readily available online.
that said, a few excerpts in the 4th movement, especially the slurred passages midway through, are a real bitch. get it right at half speed, and just keep clicking the metronome up a few clicks every week or so. i generally start at 45 bpm; then in week 2, i do it at 45 and at 60; week 3, 45 & 75; week 4, 45 & 90; etc, until I get it up to speed. do the same fingerings each time. i don't know why it works exactly, but i've found that keeping the slow pace every week (i.e., maintaining a rehearsal speed of 45 throughout, even as i'm speeding it up) really keeps me on top of the part. but you need to keep the same fingering each time.