Did you try Lucas Power Steering Leak Seal?
On two different vehicles I was told I needed a new Power Steering pump. Symptoms on both were leak without metal flakes.
I used Lucas in both and it did a great job. The leaks stopped in short order and never reappeared.
How bad were the leaks?
My experience with various types of leak stop for various purposes has been hit and miss, but it might be worth a try here...
OTOH, a PS pump with 270k miles on it can’t be good much longer, I would think, even with no flakes...?