Volvo G960 been having the issue of brake reservoir losing its fluid,when it does error comes up "service brake", I don't see any visible leaks. have pulled wheels and pressure tested the wheel brakes to see if any o-rings are leaking they all seem to be ok and hold pressure.it takes several days for it to empty the reservoir. Any other places to check for the fluid to go? thanks
Is it leaking into the booster
If it's similar to the clutch master cylinder, like on older Champions, the master cylinder has a booster attached and there is a rubber boot over where the linkage connects. If it's wet inside the boot you've got some bad seals in the booster/MC. If that's OK I'm not sure if the hoses could be weeping.
sorry was on vacation. not seeing any moisture on the booster or around it.