doesnt need to be a race car though the lt77 was built for cars, anybody with a defender knows how hot t/box can get , oil has several things to do ,lubricate bearings and gears ,cool box and facilitate gear change(which is forcing a bronze alloy ring over a cone ,baulk ring has to remove some oil to alow it to grab but not all so you have metal on metal), a thick ep gear oil might be good for lubrication as was widely used in the past but not so for easy gear change and cooling, in my experience atf or mtf changed regularly (which really is the major factor for long life) are both more than adequate for lubrication and cooling, mtf ive found does help improve gear change on quite a few boxes,though not all,the slight variances between gear cone and baulk ring contact surfaces might mean some boxes fair better on slightly different oils(hence some people find other oils better ) ,putting mtf or atf in a box wont cause noise which is caused by lubrication issues in themselves it would have to be existing problem or bad luck, isnt op complaining about noise not gear change
