Sorry to say - you need to replace the entire steering gear.
The boot is only supposed to keep dust, dirt and debris out from the gear and seals of the gear. It is not made to keep fluid in. Once fluid is leaking from the boot, the gear has a seal leak, and must be replaced. - DaveJHM
Hmm; at one time for certain vehicles in years past, you could purchase a seal kit. The problem is, just like conventional steering gear box situation, that even if you could remove the gear, rebuild it on a bench and reinstall it, you would probably have scoring in the bore that would not clean up, resulting in the need for the assembly anyway. (Many sector shaft seals that are replaced on old-style conventional steering gears leak again because the shaft itself is scored).
So, sadly enough, you are looking at replacing the gear outright. Prices aren't too bad in the aftermarket, though, if I'm correct. Good luck. - DaveJHM