500 SL (R129) Brake Question

[jgl1]

I have driven approx. a half dozen '91 -'92 500 SLs over the past several years and have found that all have what I would characterize as an exceedingly soft brake pedal feel, atypical for a Mercedes... brake action doesn't really become noticable until the pedal is depressed more than half of its travel. Its disconcerting at first but one grows accustomed to it after driving the vehicle a bit. Typically, the owners have no complaints.

Quick visual inspection invariably reveals no gross faults - pads and discs are within in maintenance limits, proper fluid quantity in brake fluid reservoir. No brake pedal sink is observed when a constant pressure is applied.

Is this typical for early R129s? Design fault(s)? Any fixes available, such as installing components from a later production year - master cylinder change? Brake booster?