Was it always running hot or all of a sudden? If its all of a sudden, maybe your fans are failing since most likely the crater wouldn't be created while it was in use. I had this issue before with an CPU. It had a tiny tiny crack and for some reason it still worked. I did some googling and there is some layer between the outside and transistors, so if it works, it'll keep working.

However CPUs and GPU chipsets are frigile. I've broke many of my GPUs when the heatsink was stuck and many CPU people broke their expensive intel i7's when they tried to delid it improperly. So be glad that yours is still functional.

Try some thermal paste and make sure the fan bearings are good. Spin it very fast with finger and listen to any noises.