Power steering leak?

I'd have to see the leakage for myself, but my suspicion is there are o-ring seals on the two steel lines that didn't get replaced. Depending on the design, the leaking fluid can build up in a cavity in the frame or cross member, and it has to build up high enough before it runs over and causes a leak on the ground that you can see. Those o-rings almost always come with the replacement steering gear, but they're in a plastic bag and have to be placed on the lines by the mechanic.

There could also be a hairline crack on the end of one of the lines. If that migrates high enough, it will spread past the o-ring to where the fluid will leak out by the threads.

There is very little that can go wrong with a rack and pinion steering gear, and you'll always buy a rebuilt assembly. You only get a new one when the vehicle is under warranty and the manufacturer is supplying it. I've never run into a problem with a replacement rack and pinion assembly, so that adds to my suspicion that something else is being missed or overlooked. I would approach this by washing the area with engine degreaser, then running the engine with the vehicle on a hoist to see exactly where the fluid is coming from. Even a real slow leak should show up as wetness that is visible after a few minutes. You may have to work the steering wheel a little as that will increase the pressure in the supply line.

The steering gear can only leak from two places if a seal fails. One is at the input shaft, and that usually results in power steering fluid running onto the carpet by your feet. The other is past either rack seal. That's by far the most common failure. The fluid will run into the accordion boot on that side, build up over time, then run through the small equalizing tube to the other boot. There's a 50 percent chance it will eventually run out on the left side, regardless which seal is leaking, the left or right one. If the fluid is leaking from where the hoses attach, there could be a tiny crack through the threads, but that is real uncommon to run into on one steering gear, and real unlikely to occur with two or three of them. A cut o-ring seal is much more likely.

The only way I could see this being a problem with the rack is if some new guy did something wrong on a bunch of them when he rebuilt them. That is still real unlikely because they're tested before being shipped. I'm pretty confident something else was overlooked.