FarmPro 2420 Hydraulic fluid

[Frenchman]

I have a 2005 2420 Farm-Pro tractor with the Y-380 3cyl. Diesel engine and I have 3 manuals on the tractor but the only info on what Hydraulic oil just says 40 ? not sure how to understand that. does anyone know if the Standard hydraulic oil for other tractors will work or does my tractor require some special oil? never had to add any since I purchased the tractor until I had to remove a valve on the side of the transmission housing to replace a broken power take-off lever, the lever is off-set to clear the bolts holding the valve on so I had to move it and the large Banjo fitting on the bottom of the valve leaked a lot of my fluid out. any help on this will be appreciated.