Familiar with the MF135, but they are very similar to the Dexta.
You do not have to split the tractor, you will have to lift off the hydraulic cover to gain access to the hyd pump.
Would strongly advise getting a workshop manual before doing anything , as there are linkages you will have to disconnect before removing Hyd cover.
Access to diconnecting linkages for preparation of removing Hyd Cover are through the round covers on the sides of the tractor below the Hyd Cover, you wil have to drain the oil
Changing seals on pump is not hard and there are kits available for the MF-135 so assuming also for the Dexta
Hope this helps