am i better off buying gears new or saving a few bucks from e-bay? i see them with under 10,000 miles. some say brand new with some surface rust.......would those be ok? also......what do i need to buy to make my 93 mark VIII rear housing into a trac-loc? can i take it into a shop and have them do it for me? or can i buy a part to go inside it? i don't know much about these.