just finished replacing the heater core as well as the evaporator core. The original symptoms were a sweet smell in the cab as well as smoke coming out of the vents. as soon as i noticed this i obviously replaced the above parts. After driving around for a few days im noticing a small oily build up but only on the windshield directly above the defrost vents (im assuming this is antifreeze.) Is this likely still coming out from before or did i misdiagnose the problem or maybe miss something else. When i pulled out the old heater core it seemed fine which kind of surprised me but the evaporator showed visible signs of having leaked.

 

I very well could be the remaining stuff left in the vents. Thats just a guess though. Run it more and see what happens.