A few years back I had a similar problem and I to read the installation manual that said use the spacers. The problem was the installation manual was incorrect, there was a typo on when to use the spacers. So if it's 68 mm do not use the spacers. I can't tell you how it resolved itself because I am not sure. I took everything apart and started from scratch and everything went together as it should. I am still baffled on what went wrong.