Yeah, I recently had difficulty separating this ball joint on my 325xit. I didn't want to use the pickle fork because it would ruin the ball joint boot. So I used the hinged, ball joint squeezer tool from Harbor Freight, like above. Worked on the ball joint for about three days. I though the squeezer was going to blow up in my face after tightening it so hard. With the squeezer on and tightened, I banged all around the joint, put some heat on it, doused it with 50/50 ATF/Acetone, etc. I was just about to give up when suddenly I heard a gun shot which made me jump. Thought I had broken something drastically. It was just the ball joint popping off, finally! No damage, but what a royal pain that was.
By the way, there is very little room to work on this ball joint. You can't even fully remove the nut until the joint has separated. I found it did help to custom grind away a bit on the Harbor freight tool to get it to fit better.