When I got my '86 300e the alarm horn under the hood had been disconnected. The only alarm indication was the flashing headlights. This worked ok in dry southern California. When I brought the car home to moist Oregon, the alarm started going off at random. Since my wife was a bit shy about driving with the headlights flashing, I just went under the passenger carpet and disconnected the alarm module. There was some moisture under there and I understand that the alarm module is sensitive to moisture.

As far as your radio is concerned, I think moisture has gotten into the control board. Maybe it will dry out eventually but in the meantime I'd suggest disconnecting the antenna with the antenna raised. Then you can avoid the up-down action and can check to see when or if the radio dries out. You might try a hair dryer (carefully) to warm up the face of the radio. I don't think Perrier water contains any sugar. If it does, the radio could be beyond any easy repair.

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1986 300E
1993 Volvo 940 Wagon
1984 Volvo 240 (daughter's)
1976 Dodge 1/2T pickup, gas hog