I Had a Root Canal 21 Years Ago and Now Told I Need Another Root Canal on the Same Tooth?

I do not have pain or tenderness in the tooth but the dentist I see now states that there is a shadow on the exray which means infection. He wants to do another root canal and new crown. I am over 60 and don't know if I should let him do this or just extract the tooth. He states that it looks like the roots aren't the way they should be and that might be why the first root canal wasn't done right. Apparantly the roots don't sit the way they should on the exray.