Joe,
12 years of service is pretty good.
But I would remove the motors and the covers on the worms. Then, with the scope package off the mount and the mount balanced, manually turn the worms - they should turn pretty freely with just your fingers. I sounds to me like something is binding in the gear train, probably at the worm to worm wheel interface but it could be one of the bearings in the Ovision bearing block. I am not familiar with the Ovsion design but you should check to make sure the lash (spacing) between the worm and worm wheel haven't shifted for some reason.
Of course you should also verify that the main bearings haven't seized. Do that by releasing the clutches and seeing how easily the RA and DEC axes turn.
Once you have confirmed that everything moves pretty freely over a wide (like 360 degree) range of axis rotation then install the new gearboxes. Based on your description it sounds as though something has seized up for some reason.
Good luck.
Mark C.
PS: If you had recently adjusted the worms in an effort to reduce backlash (which some carry to the point of a fetish) then I'd shine the Flashlight of Darkness on that - it is common for people to try to reduce the backlash without realizing that unless they do so at the point of closest mesh on the worm they will end up with binding when the worm rotates to that point hours later. I recently adjusted a (new from the factory but not Losmandy) mount where the worm axial loading was so tight you could feel the worm axis bearings rumble as you turned the worm shaft. And then when I rotated it through many revolutions so the worm wheel (on the axis)? rotated through 180 or more degrees I found a place where it bound. Obviously the assembler at the factory needed some training.
