i've got a problem with my '83 300td turbo diesel. sometimes when i start the car, i will notice that the power brakes are not working and it will be extremely hard for me to stop the car. when i manage to start the car, it will not stop even after turning the key. i have to get out and push the red stop button to get it to turn off. this usually seems to happen when first starting the car. i have yet to have the power brakes go on me while driving which would be extremely dangerous. anyone know why this is happening?

steve