I have an abscessed root canaled tooth. There is a black line around the bottom of it... I'm assuming its the dead "original" tooth underneath.
All teeth that have had a root canal are dead because they have had the blood supply removed when the nerves, and pulp were removed. The blood is what protects the tooth. They never do get all roots cleaned out which along with not being supplied with blood is the reason they become infected. This infection leaks back into the mouth tissues and can travel into the blood stream to different parts of the body to cause other problems.
I would have it removed. I have said this to others, but they always want to try and save the dead tooth. Good luck in doing that. You will be asking for big trouble.
I chose not to have missing teeth replaced with implants because of the metal. You can keep the teeth from moving around by getting a retainer made, [plastic]. $1700. Plus a few hundred getting a test done for compatibility. 4 implants were $20,000. Complete mouth of implants = $50,000. That was about 10,or 12 years ago.
Good advice is to seek out a holistic dentist. There's dentist out there that still use amalgam, and recommend RC's.
What you have done is your decision.