Thanks you have been a great help.
I was thinking about how this all happened and have a theory. There was water in the HST unit, not much, in the warm weather it just flowed around got caught in the filter or emulsified in the oil. The last thing I did before plowing the snow and blowing up the HST was to water the trees we had just planted, before the first frost and the ground froze. The Kubota got a little wet that day, then it sat in my garage for a few weeks, as the weather got cold but no snow, then it snowed and was -20 overnight and in the minus teens the day I plowed the drive. My thoughts are a small slug of water that had not made it to the filter froze or crystallized and blocked a oil passage way, pipe or even the filter, causing the HST to over pressure, blowing up the swath plates and piston and causing damage to the transmission, maybe thru blowing out a seal and bearing, I assume the HST has a physical connection to the trans thru a shaft which should have oil seals and bearings?
now what to do next, I see four options maybe more but I haven’t thought of them yet. ?
1. cut my losses, pay the dealer for his time and part out the unit.
2. pay the $8k and fix the unit, then sell in the spring and buy a acerage tractor.
3. pay the 8k to fix the unit, trade it in on a new or used Tractor at the dealer, they have a nice 2008 BX25 with front end loader, back hoe and post hole auger with 540 hours.
4. pay to have it fix and drive it till it dies.
either route I’m out $8k, but option #3 is my preference route, already planning thing I can do in the spring With a backhoe. ?