So the 1988 kit has a pair of hydraulics that are there for display, but don't actually do anything. In fact the whole assembly just moves upward with the thigh, and it looks somewhat awkward.
So, what I've done for the hydraulic system is make it actuate, just for the sake of having the mechanism "look" like it's working when the outer armor on. It's still only there without any functional purpose, but it moves. I used the injection pin marking on the the underside of the front leg as a reference to drill a hole. Through this hole I inserted a plastic rod with my two fake hydraulics I made from the sides of a runner.
These "pistons" were then secured together using some staple wire.
This is what the movement looks like with the artificial pistons, which move with the thigh.
The piping on the rear of the legs on the Nu Gundam seems to have been interpreted in various ways over the years. Originally it looked like some sort of metal coil, which was portrayed through molded lines on the older 1988 kit. The MG Nu Gundam uses mesh pipe, while the Nu Ver. Ka is just a smooth pipe, relying on the end user to detail it as he/she sees fit.
For the older kit I sanded off the molded detail and put in springs from ball point pens.