Ordered mine today K2681-21212. Ordered from Messicks. I was to order online, but suspected an error on my part, and an error on their part, so I ordered today by phone. The the nice lady on the phone helped me straighten out my part number so I would be sure to get the new/improved guard. Hopefully I helped them straighten out an issue with the costing of their Kubota mug, which is far cheaper than $133.01, and is not manufactured by Bushhog. (Not a slam..vendors pick part numbers leaving Messicks to pick up the pieces and keep it all straight.)
I just did get through working at the edge of the woods, and was a bit worried about it, thus the guard purchase. I almost always leave the deck on for the additional weight, but I needed to get closer to a building than the deck would allow, so every vine, stick, and brier received a murderous blow from my pick blade, and their relatives seemed to show up to each trial/funeral.)
I wrote an earlier submission to this thread that said that I did not see any of air flow problems with any of the applications. I said that if you are worried about it, you would be better off cleaning up the housing behind the fan to remove dirt/mud/debris. I was in a hurry and I made that sound theoretical, but I meant for it to sound practical.
When I bought my tractor (used), about the first thing I did was run it out of diesel a couple of days later. My fuel gauge was (way) wrong. I took the tractor apart to fix the gauge and did a thorough cleaning. There was considerable gunk/debris on the area behind the fan, so I would suggest folks look there sometimes to be sure this is clean. It would take a severe drop in air flow to match the effects of a filth/film/mud on that housing.
Incidentally, the problem with my fuel gauge was that it was rotated into the tank in such a way that it hit the side of the tank near half full, and would go no lower. I rotated the assembly from the top until the float would move freely top to bottom, and I sealed the area with sealant the best I could. It has been quite accurate on flat ground ever since. Results vary out and about, but there is more than adequate warning that I should be filling up the tractor. The fuel level sender is in the left tank but the actual float is in the area of the tank near the center that connects the right side of the tank to the left side of the tank, so as you might imagine, a twist one way or the other, and the float strikes the wall of the tank.
Remember, the fan protector issue is like the PTO generator issue, in that we all have different needs because of how we use our tractors. The new plate will be adequate for me, and I appreciate Kubota offering it to me at a reasonable price. Some of you fellows absolutely need more armor than that plate, however. If I had the more elaborate plates, I would blow or wash them out routinely to get rid of mud, seed heads, and whatever mice and rodents use to build their apartments with. The actual fan air will likely wind up going up and out, but the entire transmission housing provides cooling, not just the fan blown area.