I have used a GV unit between a C6 and a remote NP205 for 19 yrs. The company reps have changed, but the do and don'ts have not. They operate on a little over a quart of fluid, so use good synthetic, like Lucas, and change every year or 10,000 miles. Don't use it engaged for compression braking down hill. Lite throttle downhill is better, or disengage to direct drive. I have replaced it twice because of cone clutch failure. Very rarely use it in the auto mode, as I prefer to shift it in and out manually as conditions require. Only shift in and out under power, especially on the disengagement. They are hydraulic actuated, very similar to the British od made by Leycock. There were some IDI/Allison combo's installed as drive train in some bus models back then that were all manual. Hard to find and they were direct drive, so u didn't gain much except an in between gear.