You may faint when you see the price of a rebuilt box. New, the box is $2300 MSRP. A dealer rebuilt is $1400 MSRP, or $1100 wholesale, with a $450 core charge. Aftermarket rebuilds appear to be about $450 with a $200-$450 core, depending on the vendor.

I would consider a good used unit instead, if you don't want to re-seal it. They're under $100. Or, see how much a local MB indy shop would charge to replace the seal. A few years ago my BIL had his steering box re-sealed at the dealership, it was under $500 (about 4 hours labor plus parts & fluid).