What type of oil is used in the gearbox for the radiator cooling fans ?
I'm not sure about MCI, but Prevost uses a specialty oil, that costs about $40 a quart. Check the dealer.
I run straight 40w engine oil in my gear box.
The regular engine oil is just great for that right angle drive box.
Frank
I use a 90 wt gear oil on Prevost radiator fan gear boxes.