There should normally be a hole in the exhaust elbow with a cotter pin in it. This design normally prevents water from entering the engine. However, if it rains really badly, a roof over the tractor is still the best solution.
Change all fluids, even the coolant (G11!) will be outdated and will no longer prevent the engine block from rusting.
Water (condensation) in the oils can also be an issue if the tractor has been left outside for a long time.
gearbox, portals, steering gear: SAE 80W-90 API GL3 or 4
hydraulic steering: HLP 32
motor: SAE 15W-40
cooling system: G11 the blue one (not G12 or the red one!)
Repairing the drum brakes is not a big deal, it is well documented and the parts are readily available.
Please take photos of it, I would be happy about it.