I can't imagine that fan blade wear is an issue with irrigation motors. The aftermarket jobber I gought my Deutz parts from was actually surprised that a fan would wear out; and this guy knew Deutz like a book. Still he was able to get me a brand new Deutz "hardened blades" fan for about 1/3 of what the combine shop wanted.

A brand new fan in a combine will keep the engine running clean, with little need for the morning blow-down. Of course, attention to the tiniest oil leak is still very important. As the fan wears, air flow and pressure decreases and it becomes more of a requirement to get after the jugs and other cooling radiators on a regular basis. If you're needing to do a lot of cleaning it might be time to see how much the abrasives in your hay crop have sharpened the blades. Sharp is bad on a Deutz fan.