My thoughts. Detach the loader so you can get a good look at the quick coupling, you will also be able to take pics/video a lot better. The coupler is only locked down in the center, perhaps the housing and mounting plate has flexed already. It appears that one of your orings is leaking, if it is not seated in it's groove correctly it will allow fluid to exert pressure where it shouldn't and leak (however it may be the adjustment as noted later). When you disconnect the coupler, run a straight edge along each half to ensure they are true. Replace orings if accessible/necessary, re-seat and retest if all straight, then look at the adjustment.
Adjustment - EDIT: (May be no adjustment as noted below)
If Kubota designed it with some thought, they will have put a rotating offset pin in the coupling to allow for wear and proper clamping. So the center locking pin (or the bottom clamping pin) may well be offset and adjustable, you will have to unlock the lock nut and rotate the pin to allow some adjustment. If they didn't put an offset pin, they may have put a slot to slide the pin up/down. This will allow the coupling to be set so the it clamps into place completely. Hopefully you don't have a warped housing, and Kubota has made the clamping force adjustable.
If it's not straight, I expect someone may have reversed out too far when removing the loader. Or it could be a design fault and be of insufficient strength. Hopefully some adjustment will fix it.
EDIT: I've just managed to have a look at a parts diagram for one of these, and from what I can see, (difficult from diagrams) it appears that they are neither off center pins or slotted, so they may not be adjustable. If that's the case and yours is warped, speak to the dealer and see what they come up with. Good luck. YMMV.
