I have from time to time had condensation in my headlights and have known others to have the same too. I have read anywhere from putting in dessicant or drilling holes and putting gortex tape etc... to solve the problem. Some are successful, but I cringe when I hear these sort of solutions. I am sure some of you have hear of venting solutions from AMUpgrades for the Vantage, but they also now do it for the DB9 and DBS (08-12). Cost are discounted at the moment and for Mainland UK and come in at around £308.30 and another £39 for a 3 year Warranty opposed to the standard 1 year.
It looks pretty slick, no cutting, drilling etc... fitment time...I reckon about an hour or so.
Food for thought, given the expense of a new lamp.