If it's not the cylinder latch, you might try looking at the ejector rod where it locks up with the frame. It sometimes unscrews a bit and that makes it longer and it hangs. The rod can also be bent and will hang only occasionally.
Either way:
You can usually push the spring loaded retaining rod using a screwdriver back far enough to clear the end of the ejector rod and open the cylinder.
Then loctite the ejector rod.
Prescut