John Deere 500A Backhoe

Im trying to fix a leak in the loader valve on my 1968 500A backhoe. Its next to the hoses coming out of the top of the valve. Its
Leaking from what looks like a smooth top plug. Is it a screw in or will i have to remove the whole valvebody and pull it apart ?? Hope this pic helps.
Thanks.

John Deere 500A Backhoe