Aircraft fuel leaks are commonplace. For Nimrod there is a specific authority written down which describes the type of leak, the amount of leakage permitted and identifies areas where no leakage is permitted. There is no grey area on this! They are generally only minor leaks but still have to be documented for information/rectification. Camelspyyder is absolutely correct. He probably does fly in a leaking jet every day ( well, when he does actually get a jet to fly! ). Take a look at any of the aircraft F700s and you'll see the description, location and frequency of inspection for these minor leaks. They are not taken lightly and are carefully monitored. When the captain of the aircraft signs for it to go flying, he should be aware of these leaks ( ADF log ) as should all concerned.
To describe the jet as "leaking like a sieve" is total nonsense! No aircraft will go flying with a known fuel leak which has not been assessed. All known leaks are carefully inspected by competent tradesmen and any deferment for repair is considered thoroughly before allowing the aircraft to fly.