C5, need to clean HVAC vents.

1999 C5 Automatic, 15,700 miles

I guess this is an oft-told tale, but here goes.

A mouse moved into my blower fan recently, and then died. I took out the fan (and mouse), cleaned the fan and reinstalled. I get an awful dead animal smell with the fan on, esp. in recirc mode. I've tried spraying Febreze and Pure Ayre into the intake by the driver's side windshield wiper. That works fine as long as the Febreze is right there being sprayed through, but as soon as it's gone, the smell returns.

So what do I need to do? I'm thinking the only solution is to scrub out the entire ventilation system. How do I do that? Do I have to take that screen that covers the intake and run a long flexible brush down, with hot soapy water? What about removing the blower fan and running a brush up from there?

I don't know how to remove the little fasteners that hold the intake screen. Is there a trick for that?

I realize this is probably going to be a very unpleasant task, but I'm also hoping I don't have to take the entire dash apart.

I humbly appreciate any help!