Hydraulic Alarm and Horn

[mwgrabau]

I have a 1991 911 Carrera-4 Convertible. When I start the car after a couple of days of sitting in the garage, the alarm icon (!) comes on and the 4-wheel drive icon and brake icon are also illuminated. I start to drive, the lights are still on. After about 20 seconds, the alert starts sounding rather noisily. If I just ignore it and keep driving, the lights go off and the horn goes quiet about 15-20 seconds later.

This does not happen every time I start the car, only when it has been sitting for at least a day.

There is no fault indication in the electronic system. There are no leaks.

Apparently, this can happen if the brake pressure acculumator bottle takes a long time to fully charge. Could that be a result of the accumulator discharging when the car sits around for a long time? If yes, what could be causing it? What keeps the bottle charged in the first place when the engine is off (e.g. check valves etc.?)

My repair guy has been checking out the system and is stumped. He doesn't want to just shot-gun the system by replacing the accumulator.

Maybe somebody has seen the same problem?

Would appreciate some advice on what could be wrong!

Many thanks,
Michael