Wild guess; they filled the brake fluid reservoir with brake oil, dot 4 or similar, should be a mineral based iso VG 32.
Seals in this system don't handle the dot 4 well.
Specs according to manual;
iso6743/4 HM
AFNOR NFE48-603 HM
HAGGLUNDS DENISON HFO-HF2
CINCINNATI P68.69.70
ISO VG 32
We've had similar issues with the doosan brake systems, in the previous series.
Also we expierenced issues with drive axle oil, glazing of friction discs with the wrong oil resulting is a harsh pedal, reducec braking power and sqeeking of brakes..
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