The front calipers aren`t releasing?
Sticking caliper pistons or too much pressure?
Pressure shoudl disappear as soon as pressure on pedal released .So pressure being retained inline by either :-
1) Too long pushrod preventing full return of internals
2)Residual valves
3) M/c having internal residuals as well as external
Can you bypass the residual valves? where in the line are the valves fitted, i assume straight from the master cylinder?
They are mounted within 22inches of the master cylinder and at the same level .Unable to mount direct to m/c ,my preferred option, as they would protrude through floor .They can be bypassed as the brake system is designed to be modular now .
Is the servo mounted horizontally or at a angle? ..........You should have a slight upward tilt, between 25 & 45 deg, to prevent air getting trapped.
This is a TWIN remote servo, it looks like 2 single servos bolted back to back and mounts horizontally .
I would bypass the servo initially,
If the problem disappears then suspect either an air lock in the servo or faulty seals (unlikely or you would have noticed a drop in the brake fluid level)
if the problem persists, I would remove & bench bleed the master cylinder, refit and bleed the system (without servo) starting with the wheel furthest away from the master cylinder, then the next furthest, the second closest and finally the closest.
Problem with servo could be :-
a) Having to pump fluid about 24 inches uphill
b) Horizontal mounting creating airlocks
c)Head of fluid too much for residuals to cope with.