Can confirm what @Xulfiqar said, I'm using 1.2 liters of Liqui-Moly GL-4 SAE 85W-90 in my 5-speed Suzuki transmission, and the very first thing I did is change all the fluids. I, too, received a suggestion to use SAE 140 GL-4 in my car, but that is far beyond manufacturer spec. I've had too much oil in my transmission, as well as too little, and you can tell immediately that something is wrong.
Get a high quality GL-4 (NOT GL-5) gear oil, don't use Warco or any other weird local potion, except for Caltex Delo EP-4 (NOT EP-5) if you can find it. Also make sure you fill the exact quantity your transmission requires, no more and no less.