'04 S40 headlight condensation

A friend/coworker drives a 2004 S40, she isn't mechanically inclined and I'm trying to save her some coin. Her driver's side headlamp is collecting moisture on the inside of the lens whenever she washes her car - are there any rubber seals or closures that need replacing before swapping out the entire assembly? She has left it a while now and doesn't want it to start causing electrical issues...