can tell you 75w90 works perfectly in spain!!!lol summer or winter where its often minus 10 here in the mountains!!
and of course around 35 to 40 in the summer!!
and ibet the castrol is cheaper than the mobil Cem

ok.. today bought mobil full synthetic 75w90 2 litre gearbox oil.. discarded the old one as it was like mud..

price 12 £ / litre.. and no noise or problem with gears.. will see tomorrow morning..

and the feedback that returned me from different discussion groups is that

a) sae75w85 is the oil
b) SAE EP-80 CL-4
c) sae 80



so you decide which one you will choose

I was not satisfied about that subject and and done more and more digging on the net..

first , although mobil 75w90 makes the gears very soft it includes high sulphur.. so risky imo.. expensive experiment for me

correct and original oil is ep 80 cl 4 ..   

so tomorrow will bin the mobil..