Scratching my head...
I installed a new fuel pump and filter on the wagon (350SBC). After fighting with keeping the pushrod up while I got the pump in, everything else was no drama. I had no idea what the engine came out of since it came with the car, but with a passenger side oil dipstick, I figured early 80s. I ordered a pump for an 82 Truck 350. It came with a return port even though I don't need it. No biggie, I just blocked it off.
After installing the pump and filter, and firing it up to find no leaks, I went out for a spirited test drive. The car pulled hard and smooth. Feeling successful, I pulled the car back into my house garage and moved on to other things.
An hour later as I was walking through the house garage I could smell gas. Looking underneath, I could see a steady drip coming from the hardline connection at the pump. So I immediately pulled it back to the shop and placed a drain pan underneath. It didn't drip any more. I kept checking it every 10-15 minutes. Nothing....
Overnight.... nothing.....
The next day, nothing... so I went out for another spirited test drive and brought it back and still no leak.
I know from experience that stuff like this doesn't fix itself. So I'm still left wondering WTF? Haven't checked it today yet.