Member California here can tell you the 'leaking' troubles with the OE design too.
[The first, dealer-installed PS version shown in the brochure with the cutie modeling it].
Yeah. See how the steering drag link comes forward to push a hydraulic control, that then sends fluid in front of or behind the fixed piston?
There's an air vent hole on top, in front of the tiny piston in the control part. In the photo, top front.
When the tiny control piston's o-ring gets worn, hydraulic fluid sprays out of that vent hole when you turn left. I tore down the PS on the bench but couldn't find a way to hold the entire aluminum assembly in the vise without distorting it, while I fought the nut that has to come off the back of that control piston. I applied as much force as I dared on that irreplaceable aluminum casting, no luck.
I then got a second entire assembly that just needed the seal for the large piston replaced. That was easy. There is occasional trivial dribble from the control piston vent hole but not enough for an oil spot on the barn floor. Good enough.
Some day I'll make a wooden cradle for the original assembly so I can clamp it securely in the vise, and overhaul it. Someday.
This third-party US-made dealer option PS simply isn't up to Yanmar quality. It works great but it doesn't have the durability and simple maintenance that make Yanmar so great.