Hi, this is my problem, very likly the same your have.
My 98' Ford Windstar has a spongy brake. It is 3.8 engine with ABS.
Replaced master cylinder to start with; new brake line, new brake pad,no oil leake, but air mixed oil in brake line after bleeding 3 times by the mechanic. went to a Ford dealership, using computer bled, no help. the third autoshop checked and bled again, no idea but said they will start changing brake volve, then replace ABS, then change computer, then change everything,........ my impression is they will assemble a new Ford.
the rubber brake line extentionn looks fine. | 
