Can anyone help me with separating the headlamp cover lens?

I'm a newbie and have a request to the community. I recently picked up a 2004 S4 and noticed that the driver's side headlamp assembly has been trapping moisture and causing my xenon lamp to become dipped. My car has recently gone into the shop so I had a chance to take the assembly home to disassemble the front lens from the back housing. I was told today at the shop to heat the assembly around the housing with a heat gun and separate the 2 parts....well 2.5hrs later heating the prying the assemble is still together and as I'm damaging the back housing, more and more...I'm starting to worry whether I'm going to kill the housing and then be screwed. I was also told that they heard you can bake it...now this is where I'm putting the question out there...can anyone help me take apart the housing from the front lens will be the man....Any insight from the community on their way that separate the 2 parts will be much appreciated.

Put it in the oven for a lil bit... thatll heat up the glue then peel it apart... just watch it every couple mins... poke the adhesive to see if its warming then pull it out and pull it apart. 

I took out all the bulbs, just wondering if I should take out the xenon igniting module...and for how long and what temp do I bake it???

Yeah, take out everything you can... 5-7  mins on 350...  Check the glue to see if its getting heated...If they need more time then yeah put em in for another few mins