Cessna 170 pilot reported a fuel leak during cruise in VMC conditions. The pilot diverted to an airport and landed safely.

Narrative

After a couple of months of disputing; different rules and regulations with the airport manager of my homebase airport I had to cancel a flight due to self declaration of being unfit to fly. During the preflight inspection; I was approached by the airport manager; and I got the situation. The following day; I showed up to the airport without incident and performed a preflight inspection upon the inspection; I found my magneto cover; had been removed from the back of my magneto well two of the three bolts anyway; the third was hanging on by a couple of threads. I didn't think much about it at the time and I had the mechanic shop on site replace two bolts and tighten it down for me. I had the airport provide fuel through the service of the lineman. I finished my preflight inspection; and I departed ZZZ I had plenty of fuel to make the trip and back from ZZZ1. However; 20 minutes into the flight I look up at my fuel gauges and I'm on empty; called approach; and I told them I was deviating from the flight plan and I was going to land at ZZZ2. And that's what I did. Upon landing with the help of a couple of other pilots in the airport manager we determined that the screw keeping the universal vented fuel cap tight was backed out; essentially making it look like the fuel. Cap was functional; but in-flight allowed all of the fuel to spill out and then vacuumed it out of the other side.The airport had tools available and they provided them to me to fix the fuel cap after fixing the fuel cap I refilled the fuel tanks; and then flew a couple of laps around the pattern just for precautionary reasons; and then landed to check to make sure everything was OK after verifying that everything was in good condition I proceeded to my final destination ZZZ1.