The fluid seems like it is leaking between the large brass nut (approx. 1-inch across?) and the plastic reservoir body. This is the large brass nut into which the pressure line tube nut appears to seated.
I've read some threads about O-rings going bad on the pressure line, but I think that would cause a leak where the pressure line tube nut seats into the large brass nut, not between the large brass nut and the reservoir like I'm seeing.
Is this where that nylon seal that I've read about comes into the picture? If so, is it still available/replaceable, or have I pretty much got to replace the whole pump/reservoir anyway?
Amazingly, as I rock the plastic reservoir back and forth, this large brass nut appears to sit in a pretty fixed position. The plastic reservoir kind of shifts/rotates around it.