Why I like my M9's there is NO clutch in the bellhousing, just a damper plate to reduce the shock of going from forward to reverse above an idle speed. All the 'clutching' if you want to call it that is controlled hydraulically with a proportioning valve in the main transmission case. Last time I checked the lockup pressure on the valve last spring at 6000 hours on the one, it was right on spec in the workshop manual and the other with 4000 hours was just a tad low but I didn't bother adjusting it either.
Never had any noticeable change in operations of the units either and I do a lot of forward and reverse motions with the engine rpm up as well. As a rule other than starting out, I use the clutch pedal to initiate forward or reverse motion but when roading especially, I float the main gears without using the clutch pedal at all. That comes from decades of driving big trucks where you never use the clutch except when stopping and starting out again. I really like not having a dry clutch in the tractors as I'll never have to have them spilt to replace it as it don't exist. I believe my M9's have a synchromesh first gear however and both of mine are 12 x 12's. with the creep speeds installed though I hardly ever use them.
I believe the newer Kubota's with the hydraulic shuttles use the same system I have in my getting ancient M9's. It is a very user friendly system too and it requires very little maintenance as the main transmission fluid also bathes the hydraulic clutch packs as well as the brakes and I have a lot of fluid in the main cases. They both hold just under 15 gallons of fluid and of course they both have oil coolers mounted up front as well. With mine, the clutch pedal is optional actually. I do everything with the column mounted shuttle lever except coming to a complete stop and even then I'll just put the lever in neutral to stop the tractors. Like I said with mine, the shuttle is proportional, that is, it will gradually apply the clutch packs if the engine rpm is up so it don't jerk you and it's load sensing as well so if I am pulling a load like a round bailer loaded, it will automatically do a graduated engagement of the wet clutch pack to avoid any jerky starts. Really nice when round bailing hay. The wet clutch packs are quite robust as well. Too bad the PTO brake pack isn't. I have to be very careful with that and if any implement I have on the back don't have a built in over running clutch, I have to add one on the PTO stub. Neither of my shredders have an over running clutch so I just add one when I use them. Everything else including my round bailer does.
The weak pto clutch pack on the M9's was a bad design in as much as the PTO brake was only a 2 plate affair but I believe Kubota addressed that with later models.
I never want to have to replace the PTO clutch pack either. You can plainly see it if you remove the back cover plate (that mounts the PTO stub and gearing and while you can see it, it's not reachable and the units have to be split to replace it. I can look at it but not touch it at all. Why I'm real careful about using an over running coupler, don't want to destroy that pack ever.