Hi Norm,
When I look at the specs it says LSD rear which is always hard to push on a hard surface if the steering is slightly turned.
If the steering is straight and it's hard to push I would jack the back off the ground and spin the tyres to see any excessive resistance.
If you do have an oil leak or a problem the diff it will need splitting for repairs.
Here is the link to the manual if you don't have it already
https://www.deutschermowers.com.au/download.php?library=document&type=pdf&file=3Cheers
Max.