Once you've gotten where you need to go with USALS for any sat, can't you just fine tune and save/switch it to Diseq controlled. You can have some sats USALS and some diseq if you want. I just find that once the sat is locked in, a lot easier to adjust with a bump here or a bump there using diseq than to fuss around with USALS settings. And as the motor ages might just get more slop in the gearing or the mast becomes less perfect so USALS becomes less accurate. I know with my mast being as vertical as I can get it but not perfect (especially with temperature fluctuations) and my due south reference dubious, USALS does not give consistent or repeatable results across the entire arc.