Early GST

[Hawgee]

We have some early GST Kubota's come thru the auction yard from time to time. The Park Service units are usually in better shape than the Rental Returns. They have different options from sun shades to 4 in 1's and hours on the meter, Some meters working or not. I can see these units doing a job that would not be indefinite. Allowing one to turn them over and getting something smaller later to maintain the chores that are permanant.
I seem to recall an inherent input shaft problem in the tranny that was redesigned and updated in newer models. Some owners being satisfied with a shaft replacement. Some never having been detected.
Can anyone steer me clear of these by year of manufacture or serial number. Or would there be an amended serial number to show the update.
If my memory were to fail me, I would stand corrected. I haven't the time this week end to search old post's. Dodging the "smoke" from a burn pile between the rain squalls. Watching old "MASH" reruns @ coffee time and all.
Is this transmission something to avoid for prospective used Kubota buyers?

"What is a weed? A plant whose virtues have not yet been discovered."
Ralph Waldo Emerson (1803-1882)