I have an old GE oven from the early 1950s. The problem with it is that the oven door closes properly when the oven is cold. The warmer it gets, the looser the position of the door. At 400 degrees, a gap of about a quarter of an inch forms at the top. If I push it, it wobbles front to back. I have no idea which part of the oven would alter with the heat. Any suggestions?