Go to your Case dealer and get these Parts
1342809C1 carb to manifold gasket
B51348 needle and seat
B51463 bowl gasket
Most parts books show the old zenith numbers and Case doesn't show new numbers but I have a 1968 book thats list newer numbers that will work. I would start with these parts before buying a kit. You can still get a kit from case but I don't have the number handy(I think I thru the number away this morning :(). Most of the time it's a waste of money buying a kit. Just happens that I have these parts on the self waiting for me to take the carb off my S. Let me know if you need more assistants on this.