My '85 had a bad leak that started shortly after I began running 33"x12.5" tires. At the advice of other forum members, I bought some Lucas Power Steering Stop-Leak. It cost a couple bucks and stopped it immediately, which saves me from having to keep dumping in more power-steering fluid, until I can replace the box.
Forum members also suggested buying a PSC box ($200-$300, atleast) because replacing the seals is a pain and usually doesnt last. Also, my box is really worn and I have about 1"-2" of play in my steering wheel. I look at it as an anti-theft system...someone steals it, they're gonna wreck about 500 ft. later!!