I have a 2 wheel
M6800 with same body style as yours with somewhere not much about 1000 hours. Had issue in transmission twice, one seem to be just a bad gear and the second time had lift cylinder on disk that was leaking heavy enough ran low while disking. Keep checking the hyd oil. Odd thing is both time had problem within the trans it showed up after heavy disking for several hours, really makes me thing the trans is not built as heavy as it should be. Had a use dealer tell me the shame when were just discussing brands of tractors and he did not know I had a Kubota much less my experience. I like the rear remote control the way you can push or pull it for the remote cyl and it locks in place till the cyl had reached its limit then it kick into neutral. Also like the remote fittings the push in and put out, mine work good. The tail lights mount are replacement plastic and can be easy replaced, I have. The high range and 1 and 2 gear are not synchronized. Low and Reverse range lever is and 3 and 4th gear is at least on my trans so be careful shifting those no sync ones, they will scrap if you are not real careful, shift into and out of a synch gear first helps.
Notice you have replacement seat, for me would not have it. The style you have is not as big and thus not as comfortable as the Kubota seat and also probably you do not have seat belts either now for they mount at least on mine to the seat frame.
Two problems I ran into was starter bolts all but fell out of mine once I know (original starter) and had issue with inside batter cable post glazing over preventing good connections to batter.
I have enjoyed mine a lot, for its weight and hp it pulls with my brother's heavier MF with more HP. It is very good on fuel. Steering is very good. Engine is quite. Cranks easy. Oh, draft is to me not very good. Lift works great but draft is not a good design for plowing compared to some other brands. Dealer I bought from even told me that and he was right. My only concern is really do think the trans is not built for heavy long term pulling such as heavy disking other than that very pleased with mine. Will tell you if you run spreader with fertilizer you need to really really wash it quick and flood it, it will rust and yes keep oiling the draft and lift linkage.