'03 WRX heater core question

[abunn3]

Just wanted to find out if anyone knew anything about this before I head over to the dealership and hear their spiel.

I had my heater core go out on my 2003 WRX and I took it to my mechanic who ordered an aftermarket one for it. After he had the dash out and tried to attach it he tells me that for some reason it doesn't fit because the specific month that my car was manufactured has a different size connection. He then tells me that the only place to get a replacement heater core is from the dealership for ~$350. So instead of jumping right into that option, I had them bipass it and I'll probably end up taking the dash apart and replacing it myself. Does anyone know if there is any truth to this assertion that withing a model year there would be 2 different heater cores manufactured?

Any insight would be greatly appreciated.

[Anub1s]

Both brakes and transmissions changed mid production year in the bugeyes, so it's not outside the realm of possibility. The heater outlet hose changed part numbers in July '03, and the inlet hose changed part numbers in December '02, but that doesn't necessarily mean they are different sizes.