Before assuming the gasket is totally shot (which it MAY be), see if you can get your lump coal restarted by dropping in a fire starter through the top (with the bottom vent open).
I did this not long after I first got mine in Feb 08 and the fire got it warm enough to let me open the Egg and the felt gasket didn't tear off of the top or bottom. I still have the same gasket today. (Although it's admittedly in need of replacement NOW).
two Big Green Eggs
Custom offset smoker trailer
Smoke Hollow smoker/grill combo