Thank you TT and Wim for the answers
No TT, unfortunately my oil boltles did not have filling tubes, so I used a (clean) grease pump to refill. That was quite easy!
2013-10-10_14-38-25 par
Voucht71, sur Flickr
2013-10-10_16-48-55 par
Voucht71, sur Flickr
Yes Wim, I bought the special MT75 oil for the gearbox (an equivalent actually, but I checked it was the right one as I understood MT75 can accept only one specific kind of oil) and I bought transmission oil 75W90 for the diff.
I completely refilled the diff, and not only topped-up, because I had to drain it after cleaning it. I don't know where I read it, but I'm sure I did, that the volume is between 0.8L and 0.9L. But after refilling it with one litter of oil, I still don't reach the lower edge of the filling hole. Do you think I should add more oil until the supposed right level, or 1L is enough?
Thank