I picked up a Pre Nighthawk AT 1010 used. From what I can tell this sees to be a excellent scope for an achromat. Nice sharp stars. The issue I am having with it is the the the Draw tube is sloppy in the focuser and it will slip at higher angles with 2" accessories installed. It is the stock R&P single speed focuser with rubber nobs. Is there a way to tighten things up and stop the slip. There is no lock on the focuser. Or should I consider upgrading the focuser to a GSO Crayford? I read somewhere there was some variance in the tube diameters used over the years so that give some concern over getting right GSO focuser? Comments, Recomendations?