Just a thought on 50 hour service from a service persons view:
1. Companys are now recommending (in some cases) not to change the fluid at 50 hours. This is done so that they can say that the maintance cost are lower.
2. Having seen the material that comes out of an HST at 50 hours (after initial break in) I would change it in my tractor every time after the first 50 hours, regardless of the cost (filter too, of course).
3. I would also like to note that I am overprotective of my customers and their equipment. In theory, if you follow suggestions by the manufacturer, there should not be an issue with the product. Dispite what some people might think, the manufacturer does not want a bunch of machine failures out there, in or out of warranty. It is just bad business.
So to sum up, if it were me, I would change the hydro oil at 50 hours because I would sleep better at night knowing I did, but if some one follows the recommendations in the book, they should be just fine. Just my 2 cents on 50 hour service.