I have a 2002 Kubota ZD21. It was the model that had poor hydro capacity. I researched online when I first bought it (two months ago) and Kubota offered an external hydro reservoir. I paid the dealer $500 for parts and labor for it. I don't want to take it back to the dealer cause we all know they care nothing about our equipment like we do. Now I have a fluid leak somewhere. In addition to the fluid leak when I stop the mower I hear the fluid gurgling allot. The fluid isn't boiling from heat it will do it after ninety seconds of use. In seven years I am blessed not to have ever had a hydro issue of any kind until now. I'm hoping "piston slapper" and some of you guys that know much more than I do read this. I realize that I will have to clean this thing spotless before I start but any advise would be greatly helpful. Thanks in advance for any help.