calcified root needs root canal?

I just returned from the dentist.  I lost a filling in my bottom front tooth (nd from ctr. on left).
I have no pain, and was hoping to just have the filling replaced. Immediately, the dentist
said i'd probably need a root canal.  So x-rays were taken and he said the nerve was
calcified and I needed a root canal.  In looking at the x-rays, the two teeth next to it
also had calcified root canals.  I asked what causes it, and he said possibly age (I'm
66).  He said there was some softening of the tooth around the filling, and possbily
the filling was loose and bacteria got in there.  I have had a lot of dental work,
almost all crowns, and many root canals.  I'm just hesitant to do a root canal on
an otherwise ok tooth.  Won't I know if I get decay or an abscess?  Also, my dentist
said the root canal wouldn't be easy, but he could probably do it, because he's
very persistent.  So now I'm wondering if I shouldn't see an endodontic specialist
that I've had in the past, just in case he's not able to find the root.
Also, one more question, has anyone had a filling replace after a root canal?  Why
do I need a crown?
I'm stressing over this..don't want to spend the time or money on it right now, but
if I have no choice, I will.  Should I have a consult w/an endodontic specialist or
another dentist?

[Jerome Tsang, DDS]

If you're not completely comfortable with your dentist, it doesn't hurt to seek a second opinion on the matter.  What he says is reasonable.  I guess it would just depend on whether or not its a severe as he states.  A filling falling out is a big issue though

[nancyjean66]

Thanks for your response.  I do have an appt. for a consult with

an endodontic specialist.