I just purchased a '92 400E and discovered through my pre-purchase research, this seems to be a common problem. Mine had the same thing when I bought it, the PS leak, had it fixed and is fine now.
I also have an '87 260E with 280,500 miles and is still strong as ever. I would anticipate, assuming all things equal, it too will run at least this long, but you never know.
Last friday I headed outside to pack for a weekend out of town to find -30 degree below zero weather, and a neighborhood full of dead cars. Yes, the 260 has to sit outside. I easily drive the oldest car in my neighborhood, and with one arm, just had rotator cuff surgery, I reach in and the ole 260 starts right up. Does every morning, and purred down the highway for 2.5 hours at 80mph!
I absolutely love the W124, can't imagine another. And this is on the heels of purchasing a brand new BMW!