Well Conn1962,
I hope you got a good deal, but at the same time did you buy this sight unseen without testing the BH?
How many hours and what price? Did you get service records and last oil / hyd change detail?
First things,drive it around a bit, get it warm and work the BH check operation of the hyd pump, loader, then see whats working and not, then when warmed up, change the fluids with Kubota SUDT and fliters, and check the strainer in the suction line too.
Once thats done, and the L>R>L and BH still dont work, then the springs and detents in the BH valves may be stuck - it could be a linkage but I doubt it. It's probably crud in the valve or return detent - which is the cap at the bottom of the stacked valves. You can do one at a time or remove the whole BH assy - not a major repair but lots of connections to deal with.
Good luck with your new to you B20!
Carl