I've had good luck in rodent heater box situations pulling out the blower and probing with a narrow (~1") Shop Vac hose, sometimes attached to something like a coat hanger. Once you get the offending material out (critical), vinegar and/or good old Febreze will take care of the odor.
Thanks to our Chinese overlords, you can get an excellent endoscope for under $100. I got one from Vevor that has a remote controlled articulating camera head, which will do very good inspections in tight spots. Like, you can stick it in a spark plug hole and examine the cylinder bore, the combustion chamber, and the valves without really taking anything apart (besides removing the spark plug).