Hi to all, i own a tractor and in it's transmition it uses 60 littres of 80w/90 GL5 gear oil, by mistake my father fill about 1 litter (more like 800 ml) sae 90 (unkonwn gl), will this mix (60littres of GL-5 and 1 litter of unknown GL) cause me a problem? should i drop all gear oil and put...