Main drain - Gunite pool leaking 3" every night!?

Our gunite pool is leaking 3" every night. Ruled out skimmer basket, the 5 jet pipes (whatever they are called), ladder and pool light. The pool has drained below all these and still leaks average of 3". Im assuming main drain but how can we tell if it is the actual pipes or the seal around the main drain? We had someone come out and say that that he believes its just the seal around the main drain and it can be easily fixed with epoxy....he didnt do the expensive scopes though. Anyone seen or heard of something similar before? I realize i have to pay the big bucks to have them scope to find out the problem but i dont have the extra cash to do that or fix the pool at this point.