I'm assuming its power steering 2WD, correct?
First, DON'T try to take the steering gear apart! You'll regret it very quickly!
Yes, the steering shaft seal can be replaced without disassembly. It can be done in place but is easier out of the truck.
First, pull the steering column which is fairly easy. Remove the rag joint from the steering shaft.
The first "seal" you see is actually a dust shield. This is pressed on. To remove it take a small, sharp center punch and pierce the seal. Screw in a short sheet metal screw and pry it out.
Once that's removed you'll see a snap ring. Remove the snap ring and repeat the punch/screw routine to pry out the seal, it might be easier to use two screws 180 degrees apart.
I use a deep socket to install the new seal then install the snap ring and then the dust shield.
If you do eventually replace the steering gear, do yourself a big favor....two words, Red Head. Avoid the chain store rebuilts, they are a crap shoot at best. Red-Head Steering Gears - Custom Rebuilt Steering Gear Boxes in USA Their price is competitive with the chain stores, I sent them mine to be rebuilt, it ran $226.00 plus the UPS charges. You can have them ship you one of theirs and return yours as a core too.