Changing rear end lubricant is not rocket science. Visit your local autoparts such as Auto Zone, Advanced, O'Reileys or whatever you have close. Tell them you want to change your rear end lube and they can show you what you will need. They make an extraction tool to draw the fluid out with, then you install the new Mobil 1 75-140 fluid, no need to remove the cover. If you don't feel comfortable doing this , then ask one of your mechanically inclined friends to help. Its no more difficult than changing your engine oil.
I am willing to bet that you don't need a new clutch pack. Save the $$$ and try what I suggested.