Do you mean to carefully disassemble the dash, remove the motor, take it apart and spray it? If I were to go through all that trouble, I'd probably just replace the motor. I might try carefully applying some dilectric grease or graphite around the bearings if it were easy enough to remove and get to.

Or do you mean to spray WD 40 directly into the dash vent?

I don't think the latter would have much of an effect. Or it might, just not much of a positive effect.

(When I was younger and had much more time and less money, I cleaned and lubricated the bearings of the squirrel cage blower of a Saab 900 without removing the blower from the dash, which would have required removing the dash itself. It worked, and kept on working for at least the next 100k miles. Innovative things are possible. But I've never gotten into anything but even more trouble by spraying WD40 at electrical things.)

-Punxsutawney Phil