Mr - It all depends upon just how big your leak is.
The rack (bar that the outer tie rods mount to) rides inside the housing on bushings that will, over time wear, which creates play within the housing.
The seals can only take up so much slop before the finally start to allow fluid to seep past.
As far as I understand it, rack rebuilding is not for the faint of heart or those without access to many special tools.
Either buying a remanned unit (or having yours overhauled) is the safest way to go.

If your leak is small, you may well buy some time with a can of sealer, its designed to swell those old hard seals, sometimes it works great, sometimes not at all, but certainly worth the price of admission given the cost and time of replacing the rack.