Depends on what you are doing with the GT.
If it is a play tractor, the fan is not necessary.
If you are working it like cutting grass in hot weather or using a moldboard,
you should have the fan assisting cooling and don't junk it up with a electric fan cobble job.
just get the correct fan and while you have the driveshaft out, replace the badly worn couplings & associated parts on both ends of the shaft.
Then it will be good for another 40+years.
As far as the hyd leak if it is truly leaking at the tube nut, prolly have to replace the tube as the tight turn on one of those tubes prevents re flaring of the tube.
3/8" hydraulic /fuel line tubing from auto supply works well.
you can reuse the old nut and bushing.
Do check that the mounting bolts between the frame and rear axle housing are tight and intact also the front ones behind the hydro that hold the front of the rear axle housing to the frame
Also make sure your leak is really the tubing nuts and not the 2 relief/dump valves, just above the tubing connections.
The cleaning and baby power as mentioned, works well for tracking/finding any leak.
