Check the seal on the inner ring on the tank (not the gas valve cap that you put on to turn on the gas for the stove)...it's probably the rubber inside the gas can valve itself that is either chipped/ripped.....use a flashlight and if you hear gas leaking chances are it's not your gas CAP but the valve stem rubber seal inside the connection of your gas tank....
you can change it out if you have another empty propane tank....just use a small watch screwdriver and pop out the old rubber seal and insert the new one or one from another propane tank
It's usually a gray circle rubber that you can see inside the metal ring of the gas cylinder/can (not the gas cap/valve) but inside teh gas tank stem....
This is what I'm talking about hopefully I made sense lol....but inside the stem of the can look inside the metal ring w/ a flashlight and if it's chipped/ripped that's what's causing your gas leak and you can fix it by putting a new one of these O rings in or using an old one from an empty can and replacing it using a watch screwdriver/flathead to pry the old one out and then use your finger and thumb to push the new one in....
I had a dimwit give me a gas cylinder that leaked and i figured out it was this rubber seal on the tank itself....tried it out after replacing it with a spare seal and boom it worked with no leaks and we got to cook food!