If it is leaking from here: On that same port in the liner, you'll want to check if the middle portion of the check valve (with the spring), can be pushed down and if it is able to spring back up to the level of the port opening (see images below). You'll also want to ensure that there isn't anything that could be lodged inside of the check valve, preventing it from closing properly.
Please let me know the result of your findings and if the leaking issue still persists.