Did you put the dipstick back in, wait a couple seconds then pull it back out? A lot of times the dipstick will be low or dry the first time you pull it out and you have to put it back in and out again to get a true reading.
This is what I use. Close to 50 years old and still works great. I use it in the fall for leaf and grass cleanup. Sometimes use it during the summer if I get too many grass clippings. The rest of the time I mow with my B2920.
Here is the parts page for the lift linkage and height adjustment knob. Hopefully it helps you find something wrong with yours.
https://www.messicks.com/catalogs/kubota/rck60-29b-60-quot-mower-deck-b2320-b2620-b292/mower/a20500-hanger-brackets
Try Wenger’s in Pennsylvania. They run a tractor salvage yard along with the dealership. They have quite a lot of Kubota’s.
https://www.wengers.com/agriculture/tractor-salvage.html
We used pumps like those for decades to pump gear lube on the farm. Had 3 different lubes and they worked great. I wouldn’t hesitate buying one for other types of oil. I can understand why trying to pour oil out of 5 gallon pails gets tougher as we all get older.
Here is a link to the Workshop Manual for free.
https://www.kubotabooks.com/AutoIndex/index.php?dir=Tractor%20Owners%20Manuals/&file=L3301%20L3901%20L4701%20WSM.pdf
Dealer will not fix a tire issue on a 70hr tractor for free. If the tire went flat right after it came off the delivery truck they might, but not after using it.