If it is a sealed motor just wipe it off and oil the bearing ports if it has any. Any cleaner inside will dislodge grease and maybe ruin it. Ive soaked non sealed motors in cleaner but I would not do a sealed motor, not enough vantilation and draining to remove crud. Use a filter at the vent hood to keep grease out. It was made sealed for a reason, grease buildup-fire protection.
I have a through-the-wall kitchen fan, and the previous owner of this house apparently ran a french fry stand here or something. The fan, grate and motor are covered with grease that's grown hair. Dust, actually. The non-electrical parts are easy to clean in a sink of soapy water, but I'm wondering about the fan motor itself. It appears to be sealed, but I still don't want to spray anything on it that might seep in and screw it up. My mechanic gave me a can of spray degreaser that works nicely on my trailer wheel bearings. Maybe something like that?
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