This has been posted in two other sub-forums so no you're not seeing double or triple. Any a fellow E-Series friend/owner's '06 E350 has developed what resembles a leaky heater core smell. Pressure tests hold as they should and even close examination of the exposed heater core shows absolutely no leaks at all.

With the outer evaporator case removed for the inspection air cannot/does not flow through the core into the interior ducts---I notice the smell seems to be carried in the air stream the blower motor produces. This van has had varmint issues which might be unrelated but at this point I think cleaning the engine bay side of the heater intake including the blower motor wheel might get rid of the smell. This smell is much more noticeable when heat is required, A/C almost nothing. The heater core is amazingly clean and free of accumulated debris, cannot yet see the evaporator from all sides

Has anyone used or recommend a product for this? I've seen foaming-type cleaners you inject into the interior ducts that expands and supposedly cleans the inner surfaces, you simply suck it out with a vacuum cleaner after a while, the claim being any residual smells would be gone.

Anyway if anyone has any ideas please add them here. I'll be further disassembling the air flow components so access won't be an issue. It'd be nice if someone has direct experience with this sort of thing.

TIA