[irish1966]

Steps I would do:
1. Put her up on jack stands
2. Remove all of the wheels and with fluid in the res, have a friend pump the brakes, while u look over every inch of the brake lines. Especially where the line may rub against the frame or anything else for that matter.
3. If nothing visible then check the splitter valve at the cross-member to make sure it's not leaking (this won't be a visible leak as it will prob pool on the lip of the cross member)
4. remove all of the drums and again look for signs of fluid leaking
I'm pretty sure you will find it if you systematically look over the lines starting from the res back.

I had a shock remounted on mine and it rubbed a hole in the flex brakeline and we were very lucky to find it before someone was hurt (OL_SKOOL found it the hard way at a stop sign at the end of the street)