I had the same issue, but found that it was temperature and/or humidity related: it moves freely in the Winter, but not in the Summer. There's a white gasket between the barrel and the focuser that appears to expand and contract at a different rate than the rest of the assembly. If yours is out of warranty (as mine is), try changing the temperature and/or humidity to see if this addresses the issue. Doing so gets me a few days of free movement of the focuser, but since I don't change focus all that much (as it never gets fully stuck and slight movement is enough for autofocus), I've just been living with it.