I'm not sure about the transmission speeds Norrox, maybe check the linkages for wear, they may not be pushing the selector lever far enough to engage the others. Failing that, you would need to get a mechanic to look at it.
Mobil recommend:
MOBILFLUID 424
Service Refill Capacity: 34 Litres (see note 14)
Valvoline recommend:
FARMPLUS HYDRATRANS
Tractor transmission/hydraulic fluid that meets the requirements of modern tractors which specify a common oil for transmissions, hydraulics, wet brakes and final drives. Do not use in hypoid differentials or where an API GL-5 gear oil is specified. Check manufacturer’s specifications.
Service Refill Capacity: 34 Litres (see note 14)
I am fairly sure we used the Mobil 424 oil in the transmissions.
RnR.