The oven is the way to go, approx. at 90ºC, sharp point flexible knife, butter knife and some strong screwdriver, heat resistant glowes would be of great help too. Takes about half an hour to heat up well the unit. Later you have to go cutting the black adhesive all the way round, "to the bone", go in small steps, once it cools a bit - back to the oven. Once all the perimeter is cut, start lifting gently the edge of the glass. The important is to maintain it hot. Patience & gentle touch is essential. The heat gun can´t heat up the whole light assembly uniformly so there´s greater risk of cracking the glass, over/under heating in some area is problematic, in the other hand - oven - is much better.
