The steering box on my 1987 diesel wagon blew a seal,so,no power steering.
My mechanic advised my to get a reman. steering box for 400$ and replace the whole thing(250$ labor) insted of using the kit(30$) and reseal the old one,he said if the old one is rusted or has some internal wear it will blew the new seals and I waste my money and the labor...more labore intensive to reseal the old one(400$) and might not hold for long...what you guys think?

did you have play in the steeering prior to it going south?
If so I would replace, 250 seems a bit high for labor, but I must admit I do not know that car well, just MB steering boxes, and from experience if they are loose they tend to stay that way despite adjustment and seal rebuild.
Just my 2 cents