The end cap on the box is not something to remove unless you know what you are doing , if you need to change the seal on the input shaft it can be done without pulling that out. all the extranl seals can be changed out without box disassembly , the only thing that gets removed to swap seals is the valve on top to replace the 2 o rings under it , then readjust.

My friend just did this to his box to change the seal , he doesn't have a clue what he is doing , the car is scarey to drive now in my opinion.

If the box needs to be rebuilt just buy another one .