E91 xenon headlamp - condensation

[stevesuk]

Our drivers side headlamp unit has suddenly started suffering from excessive amounts of condensation - which seemed to start after a 200 mile (and very wet) motorway trip.

Any tips on what to check and how best to dry it out?

No visible damage to the lamp unit. A couple of months ago I changed the indicator bulb on that side, so I'm wondering if it's possible the bulb holder didn't go back in with a 100% water tight seal?