It is a heater core for sure and yes it is a common failure on these cars. What you will find is probably happening is that the core is leaking just enough to get a small amount of coolant on the outside of the core. When you start it up it heats up the core which causes two things to happen: first it causes the leaky core to heat up, expand and seal and two it causes the coolant on the outside to evaporate. So, you smell the coolant for the first few minutes during warm up and then it goes away. In my experience this is usually a fairly small window before the core takes the complete and total dump. You should go ahead and take advantage of this window and get it repaired before it takes the complete and total dump and leaves you stranded.