I replaced the pitman shaft seals in my '82 K2500 last year using the same method Sweet K30 described...
I had poor luck with the seals failing in other GM P/S boxes I replaced them on,so my expectations were not high I'd have better results on my old plow truck,seeing it has had a lot more lock to lock cycles than a typical daily driver,with the weight of the blade on the box straining it more..
|I got the seal kit from NAPA for about $15,and proceeded to blow out the old seals using the method above--but installing them proved to be quite difficult,as the leaf spring was about 4" away directly under the pitman shaft--so no room to swing a hammer to tap the new seals in...hmmm...

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First I made sure the needle bearing supporting the pitman shaft had no slop,because if it did,installing new seals would be a waste of effort & money,that would ruin them quickly..
I devised a home made tool to install the new seals--a conduit fitting I had lying around had the perfect diameter to match the seals O.D.,and I put a washer on one end of it ,it fit perfect and the conduit fittings flare nut secured it nicely--then I used some 3/8" threaded rod and a nut on the washer and arranged it so it would act like a screw jack,I put a block of wood on the leaf spring,and used the threaded rod to press in the seals..
I discovered the old seals had been installed with one facing the wrong way too,I had put a socket over the pitman shaft so when they were blown out they would just go flying..though I had the truck 16 years and it never leaked before,I was surprised it didn't start gushing a lot sooner!..
The "press" worked slick to get the new seals in,and so far no leaks..
I have bough "good used" steering boxes from salvage yards and had decent luck--probably better luck than I'd have had if I tried getting a good "rebuilt" one...their quality is hit or miss no matter who rebuilds them,I have even seen new steering boxes from a dealer be crap in more than one instance..