I rebuilt this bad boy when I had the motor and front suspension out, 5 or 6 years ago.  No leaks from it until now, but still disappointing my rebuild only lasted that long.  I'm tempted to live with it this season in the hope that about a year from now I can go to a Borgeson.  Get rid of the problematic valve, cylinder and especially all the $^^#@%$ hoses that I've replaced too many times to count.  

I lived with that leak for about 5 years, but got sick of it so sucked it up and did the rebuild.  It has held up since, but I am dreading the day it starts again.  When and if it does, I will probably do the rack & pinion also and just spend the $.  Until then, it seems to work fine (as long as I keep it well aligned and after I rebuilt the front suspension).

You can spend a little more and replace the whole unit, but it is still a lot of work to get everything off just to replace it and you still have to deal with all those hoses and the bleeding, etc.  I have also heard dubious things about the rebuilt units (poor quality and might crap out shortly thereafter).

Good luck.

 Probably can't replace that o-ring with the valve still installed???  

Dave

I've always wondered why GM used such a complicated, Rube Goldberg-ish design there.  Seems like there were other cars from the era that had the power assist built right into the steering box.  I wonder if it was to avoid having to design a power steering specific box....