Do you have a brake pressure gauge to check the pressure at the calipers/wheel cylinders???? Most folks don't bother with one, but I've found them to be an invaluable tool when diagnosing brake problems as it will tell you what the pressure is at each wheel.

Another possibility, Kurt... When it had the fire, was it in an area that would have heated up the master cylinder and the brake fluid a lot? Could the master cylinder maybe be bypassing the fluid because of some seals that have deteriorated from the heat???

Could be the combination valve, but again, hard to say for sure without knowing what the brake pressure is at the wheels........