BMW Repair: 1989 bmw 325 I heater core repair/ replacement, heater core repair, foggy windows

Question
I have a 1989 bmw 325 I . The windows get foggy and sticky after i wash the inside windows after 2 days. and the air smells sweet. I removed the console and there was no residue of coolant leaking in the heater core area. what else can cause the sweet odor and the foggy windows. would the heater core just leak a little and then the smell would be there thru evaporation?. How can i check if it is a heater core do I remove it and have it presure checked for leaks? and can I buy a used one at a salvage bone yard if it leaking?
Thanks.  

Answer
a leaking heater core is the most common cause of the foggy windows and a sweet smell. the best way to check it would be to pressurize the cooling system and check the core for leaks. i wouldn't buy a used one though. you don't know the condition of it