Good day all:
Well, I figured out what was wrong with my B7510 HST some time ago. I live on Vancouver Island and when I went to the dealer to ask about SUDT2, got a blank stare. I was then asked if I planned to take my tractor to the prairies (I grew up in Saskatchewan, I know what cold is). In the end the dealer here doesn't carry it because, as he stated, we don't need it here. So, I went home with new filters and jugs of UDT. I put the tractor in the shop and began draining the old UDT from the various drain plugs. I was very startled when, instead of hydraulic fluid coming out I got what looked like very thin grease. It didn't flow out as much as drip out with a consistency of tomato paste. About two cups of this gunk came out and then, lo and behold, very clean looking UDT. I replaced my filters and then removed the suction screen. I had to soak this for about an hour in solvent as it was totally plugged with this gunk. Sorry forgot to mention at the beginning of this reply that the tractor had started to have performance issues. Basically it seemed as though it was running low on fluid as I was losing power and had erratic operation. Well once I saw the plugged suction screen the performance issues were a no brainer. I reinstalled the screen once it was clean and refilled the tranny with the new UDT. Surprise, Surprise, Surprise, all of a sudden the tractor has noticeably quieted down and I can spin all four wheels when I'm pulling tree stumps again.
I can only guess that somewhere along the lines water was able to find it's way into the system thus creating the sludge. I'm not sure if this has happened since I purchased the tractor as I've had it in a shed the whole time other than when actually using it in the rain, Vancouver Island remember. I've done a couple of test drains on the new fluid and have gotten very small amounts of sludge out again. I'm assuming that this is remnants from before working it's way into the drain wells. I plan to pull the suction screen at 100 hours on the UDT to see if it's building up there again.
So here's the moral of the story, when I bought the tractor I watched all of the videos on what you should do when you get your used Kubota home. Yeah you guessed it, I skipped the part where I was supposed to drop all of the fluids. Chances are I could have avoided this issue if I'd followed this advice.