So I'm knee deep in the evaporator core replacement in my 95 e320 wagon. we've made amazing progress and are already on the puttin' stuff back phase on the second day of work (maybe 8-10 hrs so far.)

anyway from what i read just getting run of the mill weatherstripping from home depot is all I need to seal the interface between the box and the firewall correct? scrape off all that grey putty.

is it okay to use silicone rubber to seal up the blower motor box?

what about the flap that I guess diverts between AC and heater. you know the one, the one that is coated with some kinda of foam insulation. the blower motor side is pretty rough, the other side looks really good. what about scraping all that junk off? bad idea? what is that foam for? what about replacing it with whatever adhesive-backed insulation/foam I find?