I've got a recurring problem with my 99v70 . current mileage is 90,000 with relatively new rotors and pads, new at 70k. brakes seemed spongy a while back and i bled them with an IPD pressurd bleeder. Put in all new fluid and flushed out the old. Came out great. A few weeks later i get in the car and the brakes are spongy again. Bled them again, came out tight and responsive. Last week i get in the car again(this is my wife's so i am not the regular driver) and the spongies are back. No fluid leaks, no loss of fluid. Took it to the dealer today and he wanted to bleed it himself to start the investigation from ground zero.
Question. If it were the booster would it not be bad all the time? Same with the master cylinder ? Is there some insidious way for air to migrate into the system without a visible leak of fluid?
Have used the same bleeder and process on my 850 and the results are not the same. Once bled it stays tight and responsive.
Any guesses?