You say that you had torn rectal sprinter in 1978. Once torn is diagnosed it should have been meticulously sutured, regular follow up and pelvic floor
Now after these long years the sphincter and muscle might have lost its elasticity and tone, but no harm to repair it with latest techniques. Avoiding constipation
is the main point for torn sphincter. Where as you say that you are suffering from IBS
and you have incontinence
of motion and diarrhea
. I think with pelvic floor exercises you can find some relief for incontinence. Consulting a dietitian a balanced diet not producing diarrhea or constipation may be of some help for your complaints.
Meanwhile You say that you have internal piles coming out after loose stools, means that you have to assess the degree of damage (torn) to the sphinters.
I expect a minimum damage to the sphincter.
Consult an Ano Rectal surgeon and plan your future treatment.