If I remember if it leaks on the outer tire then it is the inner hub seal leaking because the outer seal let go or no cork in the key way. If it leaks on the inside of the inner tire and out of the drum that is slave cylinder leaking. Seems like your going to have to pull the axle /drum hub no matter what. Some times the inner hub seal leaks when the outer seal has let gear oil into the hub. When you get to pulling the axle /hub try this. Jack up truck remove axle and then bend over the locking tab that holds the outer jam nut on and remove outer nut. Now before you take off the inner nut try and tighten it first and see how far you can go till it's tight. I have seen where there has been more than one complete turn to get to 50 foot pounds. This caused a truck that was just serviced by a truck mechanic to leak gear oil. The TM tells us to spin the hub and torque the nut to 100/150 while spinning the hub then back off and then go to 50 foot pounds Then back off 1/4 turn. Myself I go a 1/8 turn off 50 not 1/4.
When you get the hub off you should see a slinger plate bolted to the hub/drum on the inside. That slinger plate slings off grease/oil out the drum slots. Make sure you clean the slots and if I remember there was three. Some time they get mud or crud in them and will not let the oil/grease sling out the way it should. Sounds like your is ok but still check them.
As for prices and best quality don't know. I would get slave cylinder, inner and outer grease seals, socket for spindle nuts, cork seal and axle gasket. Good to have this stuff and torque wrench plus this will keep you donkey covered.
