87' 5kTQ Return fuel line leak
 

I noticed a nasty fuel leak coming from the return fuel line ... near the cat (hard fuel line going through the engine bay, running down the fire wall ... at the bottom part of the firewall it joins another hard fuel line- threaded connection type joint ... that's where it was leaking - the other fuel line runs the whole length of the car joins a soft line which goes in to the tank ... Now the problem is that I was unable to recreate the leak by running the fuel pump (jumped it) .. The conditions were: got a full tank of gas, outside temp 90 deg F, drove 1.5 miles from the gas station to the house, 1.5 hours later discovered the gas leak, have not been able to recreate it yet .... Any ideas as to what might have happened will be really appreciated .... i don't really want to impersonate Evil Kanevil :)