Brakes leaking within 200 miles-dot5 fluid

AJ/FormS said
I've had Dot5 in my system since 1999.No problems, front is 70Duster KH4piston,and rear is rebuilt 69 Barracuda 10x 2s. M/C is a rebuilt,15/16 dual.
What did you use for a flushing agent?

The line to the rear should have a residual valve at the M/C, or an energizer spring in the wheel cylinder. Either system works to keep the W/C cups pressed tight to their bores

I use dot 5 in everything we have. Some sit for years, go to use any of them and they work like new. I've been using it since the 80's. Earliest was the 68 383 Fastback Barracuda with K-H 4 piston calipers and OEM drums in the rear. I can't see it being the fluid.