Others with more knowledge than me on this subject will have a more in depth answer but I believe that the GL4 is better for older vehicles , GL5 for the newer ones. Their is additives in the GL5 that can attack some of the bronze bushes. Check this earlier thread out. http://www.offroadexpress.co.nz/Forums/viewtopic.php?f=13&t=38278
Last edited by catalystracing on Fri Jul 11, 2014 10:11 am, edited 1 time in total.
some gearboxes require gl4 due to bronze syncro and bushes. diffs are often gl5 as no bronze parts in them. but plenty of manufactures make oil that will do both. there is some debate about gl4/5 oils are not quite as good as straight gl4 oils.