Call me old school, I would insist that the dealer do this or NO DEAL. If all the other tractor producing companies insist on the 50 hour service and I do know that they do and if it is not done you could VOID Kubota's warranty.
I happen to think on these lines pay $200-300 for the service or really pay out the nose for a transmission, 3 point lift, the PTO, FEL or a power steering cylinder they are all tied into that fluid. Actually they are way more moving parts that are affected by that fluid then the engine. I also think that the fluid does degrade more on breaking in a new tractor then a older one.
I have a tendency to over maintain my stuff and change the fluids earlier and much more often then is recommended, I have yet to have a failure from my equipment.
There is the old mechanic's saying pay me now or pay me much more later.