Hi All

I have condensation in the nearside headlight on a 2009 mk4 with xenon headlights. Any ideas as to why we did replace the bulbs with led ones. I have heard there are drain holes as well but where are they and do I need to take the whole thing out?

Grateful for any help

You need to take the headlights out and then check the drain/breather pipes. If you fitted LED bulbs, were they fit well and allow the rear cover to go back on properly?

Also, sounds like you have standard halogen headlights and not Bi-Xenon units....doubt you can get a LED bulb to replace a D1S bulb. 

for reference, D1S Xenon bulb shown below.

The drain holes aren't really drain holes - they're breather holes. They will be on the back of the unit, and should have short sections of right-angle tubing attached. A blocked tube can cause condensation, but also if the tube is pointing up instead of down it will let water in. 

In theory you can remove the headlight, loosen the glue that bonds the lens to the back, dry, then reassemble. However, this isn't for the faint hearted as it requires quite a bit of effort - and usually heat - to separate. When I had the issue I just replaced the entire headlight unit.