I've got a tiny stream of bubbles coming out from between the liner and the return faceplate with the blower running and all of the winter plugs tightened. I never noticed any leaking during the summer, but the only thing I can guess is a crack in the fitting. I'm considering trying a rubber plug instead of the threaded plug to see if that seals back far enough to cover whatever it is.
Any other ideas? This is bad timing for me, since I had knee surgery a few weeks ago and I'm limited in working on the ground.