Meridianauto also sells reman steering boxes. i believe it is $350.
http://www.meridianautoparts.com/

I got a slight leak on my steering box too a 91 560SEL. I tried using Lucas stop leak, and it actually got better. It has not stopped completely, but now just very minor wetness. It does not even drip/wet onto the front bushing anymore. I know I am just buying time.