Passat 2001 tdi brake warning light keeps dropping slightly over several weeks,no leeks from any brake pipes etc ,brake pads etc like new,removed master cylinder from servo,but seems dry.clutch slave was slightly damp, so i replaced it,but it still seem to drop (brake warning light comes on dash board)

SOURCE: vw passat tdi 2001 4dr

You should have a servo pump to help the pressure on diesel models. If the pump fails, then the brakes feel soft as though there is no pressure there. The other fault is, that a wheel cylinder or some other brake componant is leeking fluid. Cheek for fluid leeks and if there are none get the pump checked out.

SOURCE: reset service warning light

Try this. I can't promise this will work though. Make sure the trip meter on the speedometer is set to the odometer. Turn the key off. Push and hold the trip reset button on the speedometer and turn the key on. Hold the button until the light goes out. This works with a lot of cars so maybe it will work on yours. Let me know something.

SOURCE: on my passat ESP warning is coming on. i have

You should have the OBD codes checked. This will determine the exact fault. The ESP light will sometimes come on if there is a problem with the ABS or with the steering angle sensor.
Good luck with this
John

SOURCE: VW passat coolant warning light on

There's a level sensor plugged into the bottom of the coolant reservoir. Unplug it and clean the contacts with electrical contact cleaner. If that doesn't do the trick, replace the sensor.

SOURCE: passat 2006 2.0 tdi 140 engine won't start

Exhaust pressure sensor a possibility if it has a DPF (diesel particulate filter). Has it had its fuel pump recall, the oil pressure light could be just the constant cranking and running the battery low.