The control valve can be accessed from the side of the three point housing, you could just have a broken internal lever.
I would remove the cover and see what could be loose in the housing, I;m going to include the New Holland parts site. You will have to input the 1910 model number, and then look at the hydraulic section.
This is one of the easier models to work on, as the three pint housing does not have to be removed.
Let me know. Thank you.