Welcome to the forum, I have a 1951 Farmall M. I am restoring, I have had it for 14 years. The hydraulics is 30 wt., transmission takes 13 gallons of 80 wt...The engine is straight 30 weight, ck your manual, Tractor Supply Co. is a good source. As far as the leak, a fellow working for oreillys told me to pour a half of quart of transmission fluid in the hydraulics and it should stop the leak do to its anti-leak properties. I love my M it has a loader on front and has done me a great service through out the years. I even left it sitting out in the weather for 5 years, low and behold it started right up. Now I am installing a 6 volt positive ground Alternator, it has a 63 amp output. Changed my wiring to new wiring. I wanted to keep the M as close to stock as possible. Should be back running in a couple weeks. Good Luck Gary F.