root resection or apicoectomy?

Hi,

I had root canal retreatment on tooth #3 at end of last year. 2-3 weeks after the retreatment, I got a bump on the gum right above tooth #3. My endodontist suggested to do root resection on M-B root.. I asked him why apicoectomy was not an option.. He explained that he suspect there is crack on the root, and he will confirm that to decide between apicoectomy or root resection.

Please see the x-ray by the endodontist.

My questions:
1. Should an endodontist or a periodontist conduct this procedure. It seems periodontist knows more about root resection while endodontist knows more about apicoectomy. But nobody knows what will be needed until my gum is opened.. another endodontist told me she was quite sure it is a crack since I have a "deep pocket" on the gum so root resection will be needed.

2. Should I get a second opinion from a periodontist? (or do I have any other options?)

3. Is it possible that the root canal retreatment cracked that root?

4. Do I need root canal on tooth #4. (it is relatively less a concern. My
biggest concern now is #3)?

Thanks very much!