Probably the most common issue with our cars.

Click here:
https://www.crossfireforum.org/forum...-no-start.html

If you prefer to buy a new RCM, use an online search (Google, etc.) and shop for "2003 Mercedes SLK320 Relay Control Module". Some sites call the ECU an RCM, just look at the photo of the item, if it looks the same as the photos of the RCM in the thread above, it's the right part. DO NOT Search for "Chrysler Crossfire Relay Control Module" and buy only new modules.

I would suspect your water issue is caused by clogged drains in the channel below the windscreen.

Do this:
Remove wiper arms.
Remove the torx screws holding the cover down under the wipers.
Lift over off (it goes from one side of car to the other, you must remove the wipers first.)
Vacuum out the drains under there.
Stop parking the car where leaves and debris can fall on it.