Heater

That is a huge job that requires special equipment to evacuate and recharge the air conditioning system. Do not even think of doing this yourself until you have read the many pages of instructions in the manufacturer's service manual.

You can get a replacement heater core from a radiator repair shop, online from places like Rock Auto, and probably other auto parts stores like Napa and Carquest.

Be aware that most corroded heater cores and radiators on GM products are caused by acid buildup in the coolant. The antifreeze must be replaced every two years as that is how long it takes for the water pump lubricant and corrosion inhibitor additives to wear out.

If you decided to replace it yourself here is a great article with clear instructions and pictures for you to see how it is done.

Www.2carpros. Com/articles/replace-heater-core