I say pick an oil brand that is readily available, that you like the price point of, and is a major name brand known in most parts of the known world and then change filter and oil as recommended by the oil brand and your use of your tractor. Changing the filter with the oil when it needs changing is way more important than the specific brand you choose to use.
1/4 inch high on the stick- no worries. Chipped fan blade is your call- best thing is to not have ANY tools around when the motor is running- for future reference. You got off easy this time. If it was me- if the rest of the blade shows no visible cracks then I'd leave it alone.
Changing hydraulic oil is not as necessary as the manual states, according to my dealer- who I rely upon for this type of situation- they do NOT change the hydraulic trans oil unless it looks or smells funny. Otherwise they advise to just change filter and top off the oil at recommended intervals. Grade of oil is also dependent upon what type of service and location and high low temp range during use. A 15/40 is fine for most situations because it has a wide range. I choose to use Amsoil 15-40 diesel oil,(synthetic) due to my prior experience with diesel cars and the extreme weather I often encounter.
I too find the Kioti owner's manual and shop manual to have outdated 'UNobtainiyum' oil specs that I searched high and low for, only to have my dealer tell me they are no longer in use - someone ought to inform DaeDong/Kioti to get on the case and start printing relevant info on the spec sheets!:confused2::thumbsup: