Strange Smells

[BBBurban at aol.com]

This spring I thought my heater core was going since I could smell antifreeze 
when the heater came on.  Finally got around to getting a heater core and was 
just giving the old girl one more chance before major surgery when low and 
behold no more smell... Is it possible that there was some other source for 
this smell and where did it go?  It was only faint when it was there ... boy 
am I puzzled.  

Smell #2.  There is another smell now that seems to be exhaust that is only 
there when the engine is cold.  I see a possible leak at the pipe under the 
front seats (my mechanic says that it wouldn't be possible to smell a leak at 
that point from inside the cabin) any ideas where I should be looking?  

TIA
Hank