Aztec brake issues

[Terry3364]

I just bought a 1971 E model. The previous owner had copilot brakes installed. Since they have rebuilt the left brake master cylinder, the caliper, the parking break valve 3 times. There is no visible leaks. They bleed the system brakes are good, go fly come back and left side is very soft. Put power bleeder on and we get air.
They have bled it no less than 4 times and still it come back with soft brake just on left side.
Please help
Terry

 

[philiplane]

 

[Tweety]

 

[Terry3364]