its pretty sad that people just shove gear lube into anything that has a manual box - I had a manual transmission landrover discovery with 300Tdi come to me once for stiff action shift and noisy running after 100 kms.
replaced all the diff oils - the old ones were worse than a bad case of diarhea - when I removed the transmission fill and drain nuts I saw to my amazement gear lube draining from it - and that too lots and lots of it - about 1.5 litres overfilled, it was shiny with specks of brass etc.
Its manual but its supposed to be filled with 3 litres of DX2 ATF - After the fill the noise was completely gone - I asked the owner what he had done in the past, he told me that his mechanic used to fill truck gear oil from the gear lever hole itself as he did not not have the T-55 male torx bit to remove the filler plug and did not know that it needed ATF