The cap wasn't frozen and I was able to pry most of the cap away, but did not have the leverage to remove the part locked into the gas tank. So I decided to bite the bullet and go to the Buick dealer and pay through the nose to have it removed by experts. After paying to have it fixed, I go out to my car and find the gas door taped closed. Apparently, the expert mechanics had no idea how to release the door, so they pried it open and broke the latch. It's funny that no one bothered to tell me and I had to find out for myself. They're supposed to fix it tomorrow. They won't admit to breaking it, but it appears they are going to fix it for free. If they give me any trouble, I'll let you know.