Some wear on the shifter forks is to be expected, as you can see here on the tips. But if the wear has cut more than about 0.010 inch off the forks, you should consider replacing them. You may notice that the transmission will unexpectedly start popping out of gear if it is left alone. This happens because the forks aren't getting the sliders fully locked into position.
The tailhousing must be separated from the main case, but you have to release the connection to the reverse gear idler shaft first. To do that, knock the pin into the case and pull up the actuator.
A C-clip keeps the transmission midplate in place. It's pretty heavy duty, and Carpenter says it can often be reused if you can manage to remove it without bending or breaking it.
Once the C-clip is out of the way, the midplate is only held in place by a single bolt. Carpenter likes to check the cluster shaft bearing in the midplate by spinning the plate to see if he can feel any rough spots. If the bearing still spins smoothly, it can last through a couple of rebuilds. With the midplate out, drive out the cluster shaft. (This is the gear where all the cogs are made together.) It is located with a keyway and can only come out the backside of the transmission. Next, slide the cluster gear back into the case. Slide the main shaft out the back of the transmission. To get the clearance you need, push the sliders into Second and Fourth gears.
At this point, the cluster gear still cannot be removed from the case. First, you must press out the input shaft. The input bearing isn't a press fit into the case, so you should be able to gently knock it out.
Remove the cluster gears and clean the transmission case.