Had my fall service done yesterday (I know, a little late) and my heat exchanger has a bunch of small holes in it. This is an Armstrong Air Compak 10 that is only in its 7th year. Is this normal? The service tech showed me all of rusted areas and holes (about the size of a pencil eraser). It's costing me an arm and half a leg to get this fixed. While I'm not happy about the price, I'm more concerned about quality of this unit. Is there anything I can do to make this replacement exchanger last any longer? Thanks in advance for any advice.