I have a Dover 2-stop IVO jack that has a real bad rumbling/thumping coming out of it while running up. I found and replaced two bad guide rollers and thought I had it whipped. I know that the jack has some sort of roller guide system inside the casing on top of the car but I was a really young repair helper the last time I was involved with unscrewing one of those jacks on the cartop and probably had my mind on girls instead of learning the inside workings of the Dover IVO jack. Haha. Any description or manual on the needed repair is much appreciated. Thank you.