heater core o-rings
 

I don't think the heater core is bad (no leak in the passenger compartment) but there is definite odor and film from antifreeze in the passenger compartment. Question: can I change the connector O-rings from the engine compartment? Saw a thread on this previously but still have questions.

Thanks!

no, not exactly.

Heres a cheaper fix.. go to your local GM dealership and purchase some of their coolant treatment tablets. Plop 3 into your cooling system.
theres a 99.9 percent chance this WILL cure your issue. Im not a fan of bandaid fixes like this, but this IS the perfect situation for these to work properly.