I've not tried a small blaster as recommended by Houston54. It might work but since you're working around your vent be prepared to clean the inside of your truck when you're done. I'm not aware of any "easy" way to get into tight places. For me what works best is to remove whatever is getting in the way. In this case the cowl vent is removable without too much trouble.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.