Have you looked at the pistons lately? Wondering why you mention possible new stuff needed.
1. I've not looked at the pistons lately - when I got the calipers (years ago, now), I checked and they were fine. If you're at all potentially serious about purchasing, I'm happy to break them down and take pictures for you (or anyone).
2. I mentioned the seals because they're made of rubber and are now close to, if not more than, 20 years old. Rubber degrades naturally over time, starting with becoming stiff/hard, which is when they may start to leak. Brake piston seals are considered a wear item that should be replaced periodically, even with normal use (I think Kawasaki recommends every 2 years!). These calipers' seals have been on a shelf for years with no fluid contact, so they're likely dried out and not performing their function, today. In fact, I don't know that these seals are bad, I just know I'd replace them under these facts before installing the calipers, possibly/likely finding a leak, then having to pull them off/apart to fix when they're full of fluid.