Redo AVR - risks

My father ( presently aged nearly 66 years) had by pass and  valve replacement in sep 2006. The replaced valve was  " # 23 carbomedics ".  
Now due to severe paravulvular leakage in the valve, the doctors are advising redo AVR i.e. 2nd operation and get the valve replaced again.

We need advice regarding the following so that we can decide whether to go for 2nd operation or not:

1 As compared to the  operation, how much more risky is the 2nd operation ( my father is 66 years)? .
2 What are the chances of success of the 2nd operation.
3 After the 2nd operation, what are the chances that my father's quality of life will be better than at present.
4 What are the chances that he will have even more complicatiions after the second operation.