i sort of have the same thing...but to a much lesser extent. and ive replaced my evaporator, heater core, have a different blower motor. and my ACC works great - except for a slightly fishy smell that comes about when the heat is first turned on.
ive stuck my nose up in and around the blower motor area and i can smell the smell, but i cant tell where its coming from.
so my point is troubleshoot carefully before proceeding - i don't know what my smell is from but i know what it isn't from - all the usual suspects.
i dont know how to troubleshoot any further...i dont know whats left in my system to be making fishy smells
where does the venturi that goes into passenger side panel go? i havent stuck my nose in there yet.
and on the topic of rodents - how could one get into the evap box other than through the AC condensate drip hole? and only the smallest little field mouse could fit thought there, but it would be tough. plus the critter would just hit the evaporator and couldn't go any further.
dd