in reply to what are all the possibilites for memory leaks ?
I don't have much experience with mod_perl or Apache::Leak, but in Tk , Gtk2 gui programming, and commandline programs, objects can leave a non-zero ref count so they don't get destroyed when leaving the subroutine. I usually make a point of always trying to reuse objects. If you read their docs, there usually is a way to clear out all user data and start fresh. Then you can make your objects global and fill them with fresh data on each subroutine call.
But you don't any code, so we can only guess.