I have ball lock QD's and have been using them for about 6-9 months now. They used to slide right onto the post and come off quickly and easily as well. Now they are much more difficult to remove. It seems they pop up slightly and then it takes a lot of effort to pull them off. Everytime I change the keg I clean, sanitize, and lube with keg lube. Is this a sign that the o-ring needs replaced? Or is there residue buildup inside the QD causing sticking? Anyone experience this?