Why is my 20 year old root canal with a crown hurting on and off?

Can I just leave it alone? Pain is now very minor. It is twenty years old and has a crown. My general dentist wants to extract the tooth. I then went to an Endodontist who didn't even bother to open my mouth to look at my tooth. Instead he looked at his 3D x-rays and told me that I have a "cracked root that's causing infection in the bone. The infection is eroding the bone causing some bone loss." He said to extract it. My tooth has not bothered me as it has before; maybe it's because the nerves are dead. But why is the pain on and off?