ABS / brakes problem

[Benz300]

Guys,
I figured I'll ask this question here since the lexus forum is of not help in this matter.
Given ABS technology is kind of the same with perhaps different brands perhaps I'll have better luck getting this answered here.


1993 Lexus LS400
problem: spongy pedal, not so effective brakes.
the brake problems all go away after I engage the ABS or traction 3 or 4 times manually. the pedal feel and the bite in the brakes remain for a day or so and the pedal goes back to spongy, extra pedal travel and loss of brake bite. I have to keep on activating ABS by driving in reverse and hard hitting the brakes to keep the brakes at their optimal.

parts changed so far:
brake booster
master cylinder
all the callipers greased
brakes bled several times, last week got the ABS system bled by the dealer

no change at all.
One of the private shops suggested that the ABS pump could be the cause of this problem. However the Lexus dealer said that the ABS doesn't come into action unless ABS is activated. The private mech. claims that with this system the braking system at all times has to travel through the ABS pump which in turn sends the brake fluid to the 4 wheels.
quesiton is, can the ABS pump be causing this ? If someone has a diagram of the system perhaps they could post this here. I would like to make sure this coudl be the cause before investing 1750 in the pump and 5 hours of labor.