how do you permanently fix the water problem to the bcm? it is in shop 2nd time

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Last year, the lights and locks stopped working along with the horn going off non stop. ad it in shop they said was grommet and bcm. had those replaced.2 days after it was out of shop washed it and did the same thing. took it back they reset the bcm. it was fine up to 4 days ago when the exact same thing happened. What is the permanent fix as car only has 66,000 miles?