You say "gear box" I assume you mean "steering gear". What seal is failing? There are two large seals that must be replaced. One on the steering shaft and one on the pitmann arm shaft. There are several smaller ports that use O rings to seal. So my question to you is what seal is failing?
I have seen corrosion (rust) on the shafts which will cause the seal to wear out. I cannot see why the pump needs to be changed. There might be some sort of restriction in the return line which might cause excessive steering gear case pressure. This pressure might cause excessive leakage.
I overhauled all three of my steering gears and had no problems with leakage since. Maybe they are putting some "stop leak" in the fluid and not really overhauling the steering gear.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k