I just tackled this job. My symptoms were identical to the OP. And like another poster, I found the rubber grommet missing and that's where the brake fluid was leaking. I just want to share tips from things that held me up.
First off, my metric flare nut wrenches I used on the lines coming out of the master cylinder didn't work. You'll need a 7/16 for the two lines coming in/out of the unit (and yes, get flare nut wrenches. They are worth it!) And the mounting bolt is a 10mm.
The line from the MC was easy to take off for me. But, the line going to the rear of the vehicle was super tough. The unit kept twisting away from the frame rail all while the line wouldn't budge. The bracket that mounts it to the frame is only a u-shape, so that's why it twisted. The solution to avoid that was a 6-inch c-clamp to secure the ABS unit to the frame rail from the outside. Voila! The line came right off.
And I didn't follow the Hayne's manual order of re installation. The lines might have bent a bit because of my attempts without the clamp, so I put the lines on first before mounting the unit to the frame rail. After that, it's a piece of cake. Bleed the system, etc. Good luck to those of you that need to do this repair!