I got the same letter for my bx25d. Different ref number. Kubota didn’t know why when I phoned. Issue was with over flow cap on cooling system. That was addressed years ago.
I had the same problem. Turned out there was a Little Rock ( approx 1/8 in in dia) between the linkage and the frame. Wouldn't let the peddle go all the way down. Couldn't see it. Couldn't feel it. Blew it out and all was fine.