I agree with this post.
Toyota's workshops may have good mechanics but taking their advice can be dangerous sometimes. Because when I took my 50K driven car to Toyota, they silly people poured 20/50 petron and claiming it’s the best toyota's oil for JDMs. I still feel bad about myself why I allowed them to pour this oil at that time. Anyway we all learn from our mistakes.
Ok, if I have this car and don't know how much gear oil to pour, then I simply buy 3 bottles (each 1L) of gear oil. First drain all the gear oil with help of worker/mechanic, clean/wash the gear box with kerosin oil to remove junk properly of previous oil. Let it "FULLY DRY" for 20~30 minutes and then close again. Pour 2 bottles of gear oil and check the level with the dip stick. If its low, then I used the 3rd bottle and keep checking it till the level become full. And after 3 bottles, still if the level is less, then I must buy another bottle and pour 100 ml by 100 ml and keep checking the level till its full.