Are the headlamps sealed beam or like my 200 are they separate bulbs?
I often find water in mine after steam cleaning under the bonnet after a off road session.
Thinking about it they cannot be sealed beam, if they were and water is inside then the unit would blow as the vacuum is gone I am such a pratt at times!
In that case do you jet wash the engine bay?
There is a rubber around the bulb retainer, mine is there but it often lets some water in.
To fix just take the headlamp bulb out and leave it to dry itself out.
The fix is easy, just put some silicone around the rubber cover where it meets the headlight, the rubber is tight on the bulbs so should not leak there..............however, you try and replace a bulb a couple of months later and it is a bugger to get the cover off, made worse by the access to this area.