All new cars are initially filled, automatically during assembly by a process called Evac & Fill.
Starts by 1st pulling a vacuum on the entire brake system at the M/C reservoir. Then locking out the vacuum. While vacum is maintained on the lines, M/C, etc., the brake fluid is introduced under pressure.
ABS and ESC systems introduce a lot of possibility for trapped air due to the M/C not always being the highest point in the system. 914 is similar in that the bias valve lines are higher than the M/C and are a prime place to trap air and notoriously hard to bleed.
Obviously it's not entirely possible to duplicate that sequence at home.
However, I've found a lot of success by using vacuum on the bleeder 1st and then apply the Motive style bleeder under pressure. Mighty Vac works well enough but I prefer to use a constant venturi vacuum source like HF vacuum bleeder or A/C venturi vacuum to keep constant vacuum on a bleed screw while brake fluid is introduced at the reservoir under pressure. Mighty-Vac has only limited vacuum capability and you need to keep constantly pumping it to try to keep up with the fluid introduced - sort of a losing game.
There is always the possibility of a cut seal lip internal to the M/C but is highly unlikely. Line flex is not the issue. Fluid is displaced inside the lines. The volume inside the line is more or less fixed regardless of whether the line is straight, bent, or flexing as you apply the brakes. Yes, there is a tiny variation in volume as a line flexes but it's insignificant and doesn't account for a soft pedal.
@mb911