All of the Ford non-powered hydraulic brakes use a mineral oil based fluid. The old fluid is clear, the newer fluid is green (about 1990 and newer) colored. NH always said both would work but they do still sell both the old and new fluids.

DOT fluid will soften the slave piston orings and will cause brake leakage. ABSOLUTELY do not use DOT fluid in any Ford/NH tractor brake system. Once they start to leak internally you have to pull the axel trumpet housing to change the orings.

The other posts are right. You do fill the master cyl resivoir with the dipstick tube. After the 8630,8730,8830 came out the brakes were powered with the transmission hydraulic oil and did not have a separate resivoir.