Based upon your description, and what has been done, I would consider replacing the mechanical fuel pump (lift pump). Easy to spend someone else’s money, but $115 isn’t too bad.
Changing 17 year old lines and checking the fuel filter housing are both cheaper possibilities. I don’t know what line size a B2910 has, but my last 3 kubotas used 5/16” I believe, it’s usually printed on the line.